If you are interested in victory conditions, here is an article with some interesting reflections: https://explorminate.co/seals-victory-in-age-of-wonders-3-mechanical-wonder/
A few of my own reflections on victory conditions, though they may apply more to full-on 4X games:
1. I'd want them to kick in/be achieveable reasonably soon after it's clear who has won. Some way of forcing the remaining players to challenge you without resulting in long downtime of event-less turns/play time.
2. I'd want some flexibility to achieve them. I find it unexciting if in the first 10% - 20% of a game I already need to decide what victory condition I pick at the end. Let me build my engine first and then decide, based on how the game goes, what will be the most effective way to end it.
3. Shared allied victory would be nice to not force pointless wars at the end.
4. Similarly, I liked the concept of a diplomatic/peaceful victory, focused on gaining allies. Maybe minor factions can play a role here.
(Linked that, not really a VC, it would be nice to take over planets through means other than military e.g. culture.)
5. The research victory was ok in Sins 1. It was the turtle victory to bring a stalemate to an end. Maybe something involving one or more structures to make it easier to interrupt?
6. Rise of Nations did a Wonders victory which was also a nice touch to control when the game would end.
Gotta go but I might add a few reflections another time.