I'd just prefer ALL victory conditions be kind of "end-game crisis"-ey
Like maybe once you own a certain fraction of the galaxy, all the other empires just gang up on you. I guess technically that means YOU are the end-game crisis, but that seems kind of fitting. That'd be how you get a conquest victory.
Some sort of diplomatic crisis, like a series of votes to consolidate your federation into a singular state like the Trek Federation, mechanically similar to the EU holy roman empire, with the failure condition being your federation fractions into the constituent parts again. You'd need to have like, everyone or nearly everyone in your federation to count as a victory, and those would be parts of the vote conditions. Diplomatic victory (I actually really want this now.)
A tech victory crisis would have to be techy, and solved via tech. (Since the other crises are solved via their respective style of winning, diplomacy, military, etc) Whether that'd be a nanoplague/grey goo from a failed attempt at true post-scarcity, that you'd have to research the cure and then apply to each affected system, and which would spread through the systems via fleeing survivors. Or possibly the previously Transcended species are a little miffed you're moving in (after all, maybe not all fallen empires stayed around in the Materia, eh?) and you have to somehow disrupt them a la the Sangraal from Stargate, or communicate with them to say "Hey, yo, we just wanna live WITH you, not take anything away!" either way you'd need to research that technology before they wipe you from history. (Obviously it would have to be multiple different techs along the different tech sectors, and each tech unlocked would cause events and different responses from the grey goo/ascended nerds.)
It'd be a simple matter to re-code the current crises to be have a "YOU ARE WINRAR, CONTINUE PLAYING Y/N?" pop up once the crisis is over.
Depending on how they flesh out religion, a religious victory would have to involve spreading your faith by sword or by word across to every planet (every pop?) and eventually there would have to be a proper ending apocalypse/rapture as all good religions have, which you have to.... I'm not sure. Fight? Accept? Merely survive? Maybe instead of a rapture (since that would basically say "Yes the religions in the game are All True" which Paradox seeeems to be kind of skirting?) Maybe a crusade against the remaining heathen civs (who are too stubborn to change and so you need to crusade once the event fires) that you need to convert. Similar to the conquest victory except they have the option to convert to your religion, and similar to the diplomatic victory because you have to cajol and convince people to lend aid to the cause, you probably don't own everything. ... Okay you probably do. This one needs a bit more work.