One of my biggest complaints about Stellaris is the lack of a continuous zoom from the galactic level to the solar-system level. I would hope though that the Star Sectors feature on Galactic Civilizations IV will not make the user interface more Stellaris-like? It's a real pain on Stellaris to only be able to interact with one solar system at a time.
What would be very cool though is if the Star Sectors feature could be used for multiple galaxies. For example, after you've conquered a single galaxy, you could then discover a means of intergalactic travel, and begin conquering other galaxies, as well as researching Kardashev Type Three technologies (only available to civilizations that can control entire galaxies, as opposed to individual star systems).