I agree with your opinion.

Absolutely fine with killing off the battle viewer.

The central issue with the viewer for me was always "Well, we've given you a ship designer to design your fancy Tiger Shark frigate with it's lasers and missiles and defences and everything, now, don't you want to see how it does in combat? Of course you do!!"

As Devildog_FF says, if you can report on a battle with relevant stats so that the player can see the basic information of how well their Tiger Shark frigate went against that Drengin fleet fill of laser beams and make it look flashy enough to please most people (I'd be happy with just: 1. Notification that my frigate is approaching/being approached by an enemy and stats for each ship involved in the engagement, 2. Request for order - attack or retreat and then 3. Subsequent report on result of order, frankly), why not...

Especially if battles and invasions are going to become a multi-Turn thing. Yes, I want my forces to Invade the Drengin Core World and I'm fine with the fact that it's going to take 5 Turns to achieve that invasion. I just don't want to see a Battle Viewer/Invasion Viewer five times...Notification of how the battle's going suits me fine.

I'd be ok with that if we could control combat manually, but otherwise I like the viewer personally

I hardly ever watch the battle viewer.  It feels like a waste of time to watch a battle that has already been resolved, and which the player has not influence over.  If we could give general commands (close range, hold range steady, retreat, etc) then it would be worthwhile to have, otherwise it's simply an engage fleets, check results, continue with turn.

I love this idea of zooming in to see the actual fleet battle! What I'm envisioning based on your words sounds like it could be very appealing if the AI, visuals, effects, audio, camera controls, etc. are all up to par with the rest of GC4's polish.

I love combat in my games, SotS is one of my all-time favorites and still unmatched in some ways with how it made combat engaging and interesting. I've enjoyed combat in all sorts of other titles in this genre. 

I must admit I did not care for GC3's combat viewer, its controls, the graphics, the effects, etc. The combat experience wasn't fun or engaging and I would avoid it after a handful of views. I really tried to enjoy it but ultimately skipped it for the strategy layer animations.

I hope the idea of GC4's combat viewer eschews that for something new, even-if classic, like a locked isometric RTS view. Would this be 3D movable (with customizable controls)? Side/top? Isometric?

I do agree that battle stats intel is critical to display in a readable & useful fashion. It would be nice to see epic ship designs and researched tech builds be shown off in modern GFX glory. If it can't be given the level of detail and polish to be at least visually fun and engaging, I'd be fine with the existing "zoomed out" strategy layer summarized combat.

But if you pursue combat in GC4, mayyyybe interactive/controllable if/when zoomed in? Yes, I realize it's quite the pipe dream but one can always hope.

I used to watch the battle viewer in GC3 about half the time, but I really wouldn't miss it.

My problem with the idea of the zoom in function is that battles that don't take place on the players turn could be missed.  

When it comes to GC III's battle viewer their where a couple things that frustrated me.

1. Endless pop ups for battles of no real consequence.  I hated unlocking the tech that gives +3 fighters to each planet.  The A.I. struggled to understand what was going on and every turn would be filled with 5-10 pop-ups of the A.I. destroying those 3 fighters over and over again.  That being said I think the issue could've been fixed by removing that tech.

2. I think the animation was good when you put time in to learn the controls.  I didn't like how the ship starting placement was laid out.  Tiny, small, medium, large, huge.   It was difficult to keep ships the right speed so that the huge weren't completely left behind.  Fleets should stick together to be more effective except for support ships.

3. Fleet composition isn't really a thing in GC III.  Mixing ship sizes rarely helped, but it does add more of an epic feel.  The problem is that the very similar fleets duke it out over and over again.  In my the past games the A.I. build almost exclusively carriers.  The battles play out the same every round so I skip them more often. 

4. There's not enough uncertainty in battles.  There's rarely an upset or unforeseen loss in the battles except for those rated uncertain.  A little more randomness in battles would help liven combat up.  Critical hits that knock out ship systems or do higher amounts of damage is one possible method.

5.  Information could be better condensed.  I don't usually want a play by play breakdown.  A list that tells me how much damage was done by a ship, how much damage that ship took, and how much of that damage was blocked would be a much more concise way to present the battle information and inform my future fleet design choices.

I think all of these could be fixed without removing the battle viewer.  I'm not sure whether the zoom in function is a great idea to be honest.  I'd rather just have the option to toggle the viewer on and off.  If we can adjust criteria for what would cause the battle viewer to pop up, that would be even better.  Criteria could include player minimum logistic points and whether or not a player support craft is under attack.

This is fine but.. and I have stated this on Discord:

The player will have multiple survey reports AND will finish techs. The player cannot close any windows or zoom to any part of the map until the player picks a technology. Also the pop ups for surveys also prevent the player from viewing battles on the map.

Please disable the mandatory 'pick a tech immediately at start of turn' and allow the player to do his surveys after he views a battle or MOVE the survey event to the end of the turn.

I am all for the viewer being on the main map. Best idea ever. Just move or disable the tech pick pop up or move it to end of turn and change the survey reports to be when the player wants them.

I like the idea of seeing some sort of battles (part of the appeal of why i like space 4x games) - how that happens either through a viewer or 'zoomed in' option I don't really mind either way

I don't think the game needs a battle viewer. Just like you said in an earlier post about Stellaris, one of the things that that game does well is that everything happens on the same map. That being said I think there needs to be some level of player control if battles would happen on the main screen for it to be interesting. Some examples could be:

1. There has to be some level of player control but decision making should only be at the highest level, complete control wouldn't fit GalCiv I think. This could be gathering information and picking the general approach to the problem. Most games give way too much information for free and most of the times perfect information too. The next step would be how to decide on a general strategy. Like in the 4x game Oriental Empires you pick the composition of your armies, how those units set up (front row, back row or flank, center) and what they are going to do when encountering another army (rush in, flank, get in range and shoot, stay back or in reserve etc.)Maybe the different leaders in the game could also influence the behavior of your fleets in some way. For example you could have an admiral that simply refuses to withdraw even when he is losing. Or maybe a planetary governour organising a resistance on their planets or within the same system if their planet has been captured.
2. Unstack the fleets, perhaps ships can only flight together in small squadrons, maybe their composition and position could matter in some way. Like keeping carriers in the back surrounded by screening ships. Or maybe ships could have a line of sight that can be blocked by planets and other celestial bodies, this could allow for surprise attacks if you can hide some of your fleet.
3. Spread battles across multiple turns, perhaps there could be specific victory conditions, like capturing a planet. Withdrawing should also always be an option I think.
4. Make all the objects on the main map interact with the battles in some way. Perhaps planets with defences should be able to fight back. Maybe combine invasions with fleet battles and let both play out at the same time across multiple turns. Some celestial bodies could be more suited to place stationary weapons, like bodies without an atmosphere. Maybe being able to capture those could force other planets within the same system to surrender.
5. Perhaps there could be a logistical component. Although I'm not too sure using actual fuel would be fun maybe the different weapon types could be more distinct. For example rockets could be really powerful and super strong long range weapons but they could be limited in the amount you can carry before restocking. Or maybe there could be rockets that could also be used against planets with an atmosphere those could be even more expansive but you would have more uses for them. Lasers could have the advantage of instantly hitting their target but they would only work short range and require a lot of power. Mass drivers could posibly be the low cost low tech option but their drawback could be that they are useless against any planet with an atmosphere and that they are affected by anything with a strong gravitational pull.

In short I think the idea of scrapping the battle viewer is fine but there has to be reasons to have the battles happen on the map. The battles in the game should be intergrated into other mechanics. A final thing I would like to add it that maybe ships and especially the bigger ships should be a bit more durable and less expendable in this game. Building those and losing those should be a big deal. It might help to make some ships be important entities of your empire too. In Hearts of Iron 3 you can designate a ship as pride of the fleet which makes the ship perform a lot better however if it's sunk your country will suffer a morale loss, I think this is a nice touch and similar mechanics could work well in a game that lets you design your own ships.

Hmmm that is an interesting question.

I will have to see the alternative to battle viewer before deciding.

On the other hand, what is the point of ship building, spending hours playing with components when you can't even see it the ship you just build?

If it has no interaction ala retreat,cards I see no need.