Standalone DLC after Supernova is released.

That's a hard one to answer.

As a veteran, I'd say it would be much better to focus on the base game now and get it all fleshed out. Furthermore, it will be much easier to make a DLC campaign interesting while using the various game systems, with these systems in place and working as expected.

Looking at this from a new player perspective, a campaign could be a great way to get exposed to the game and learn the basic gameplay elements. Maybe a compromise for Supernova release would be to put in place a sort of Tutorial map, a pre-generated map with a fixed difficulty, starting point, starting civ, etc. with a lot of guidance along the way to get new players going ?

Focus on the game mechanics... there's time for a good story later

No way. I never play campaigns in any 4X game. I love the GalCiv lore, but I'd rather the games story emerge from my playthroughs. 

On a side note, an GalCiv animated movie would be really neat!

DLC.  Look at the latest Spellforce.  While people love the mechanics, it got dinged due to the requirements to play through the story each game.  You can only play through that particular story so often, no matter how good the mechanics are.

With a campaign, a subset of maps and rules that you can curate to ensure a good experience throughout your constant mechanical upgrades, you could provide a nice glimpse into the story that sadly tends to disappear during the actual gameplay.  Look at your timeline with the current Drengin start.  They don't have their race embargoed.  They don't have Subspace Scanning or Streaming.  They have no real tie to the narrative you've built.  Same with the Thalan in Galciv 2 and 3 in a standard game.  

After you have the game mechanics, pacing, events, AI and other features in place, you'll have the foundation to build better scripted scenarios and campaigns.

I think instead of a campaign like the old games had there should be a large premade "canon" map that basically "the story so far."  So you would have things like the drengin starting with kona occupied but a bunch of planets in another sector that no one besides the navigators has mapped out, various factions starting with certain traditions already unlocked, maybe a war already in progress, ect.  Then each faction would have its own objectives they can complete to earn prestige and advance the story in whatever way you want to advance it.  Basically what paradox does with a lot of their games but more organic and possibly assisted by aliengpt.

I'm personally not for a campaign.

I would much rather see focus put towards the sandbox aspects such as adding new features that improve that.

I do love the lore of the game and I want to see more lore, but a campaign creates a forced storyline where what will happen has pretty much been layed out, I just have to follow along.

I would rather see story elements added to sandbox mode instead.  (I would expect these to be DLC with maybe a new race or two with new ship parts)

Three ways I can think to do this are war goals,  fleet admirals, and expansive galactic events.

I discussed war goals with you in the past, but when you start a war you get a random set of goals.  These could be:

- Capture a the capital of the enemy civ

- Kill enemy Admiral X

- Destroy X enemy ships (X is based on the number of ships they have at the start of the war)

Fleet Admiral are leaders that can be assigned to a warship.  They could give bonuses to their fleet and ship as well as an A.I. generated name for both.  The A.I. would actively attempt to keep this fleet a doomstack.

If the fleet is destroyed the Admiral is killed and the player must wait X turns before assigning a new one.

I would recommend replacing campaigns with Expansive Galactic Events 

Expansive galactic events could be multi part events that occur over the course of a game for example:

Return of the Dread Lords

First Event: Advance Scouts (Occurs early in the game)

Spawns a couple hostile fleets made up of a few fighters and one frigate in every sector.  These fighters and frigates have the highest tier weapons and defenses that don't use special resources.

Second Event: Testing Defenses (Occurs when players have researched most mid level tech)

Spawns a couple of hostile fleets consisting of mostly of medium and small ships with one large ship in each fleet.  These ships are decked out with the best non special weapons and defenses)  These fleets attack shipyards and enemy fleets.

Finale:  Revenge of the Dreadlords (Occurs when terror stars are unlocked)

Spawns a Terror Star protected by fully stocked mixed fleets of all types of ships in each sector.  Ships utilize the best special weapons and defenses in the game.  The goal of these fleets is to wipe out all life in the galaxy.  

First of all, I thought you said GalCiv IV was going to abandon the campaign concept all together and tell mini-stories thru game events itself.  Those would initially be simple but more complex campaigh-ish ones would eventually be introduced.

Second, if you do make a campaign, please devote more resources to the ending.  I actually completed all of the Gal Civ III campaigns and they were very enjoyable but the ending of the Retribution campaign was the most anti-climatic letdown I've ever seen in a campaign game ever.

Well, if you gotta, I'd recommend DLC for a campaign.

All of my GalCiv experiences over the years have been nothing but sandbox.

No.

Add story elements to the sandbox ala AlphaCentauri.

I would rather see story elements woven into the sandbox rather than having a bespoke campaign. Give us a chain event to uncover an Arnor ship or a leader, give us an endgame crisis with Dread Lords. Let us uncover the secrets of the universe when we scan anomalies. Give us objectives which when completed uplift minor races to major in the next sandbox we play. I would much rather see you guys focusing on polishing the sandbox than wasting time for a multi mission campaign.