So far in contemporary, science endgame either by all end game tech or space race reign supreme. Why? Simply because you get more fame out of it (regular era stars, competitive deeds of completing the satelite, 300 fame for each end game tech, and competitive deeds of winning space race. Oh and each project gives fame too so yeah) and it is way quicker compared to conquest. Aesthete and mercantile don't even have their end game condition, so contemporary mercantile and aesthete is already at heavy disadvantage of not being able to close the game besides the pollution endgame which is often disabled and even then can be meddled by others trying to delay it, and for aesthete they have competitive deeds spreading influence over a continent, but that's it. Mercantile doesn't even have competitive deeds. Diplomatic is hit even worse, being the hardest star to get and no competitive deeds.

So I propose to add endgame conditions for cultural, mercantile, and diplomatic culture. For example maybe for cultural can be the classic spread your culture across the whole world, with competitive deeds for each empire covered. For mercantile maybe having x amount of gold in bank and for every milestone in contemporary era you get competitive deeds. For diplomatic maybe overhaul the humankind congress and have some sort of game ending voting like manage to convince others to vote for international disarmament, with competitive deeds for managing to push some irreversible change in the congress. For conquest they already have end game condition of vassalizing all other player or elimination, but maybe add competitve deeds for each capital captured. All of this are very rough ideas but anything to make culture besides science focus one to close game and to match science fame generation via their project. 

Yes, in my games, even without picking up scientific civilizations, I end up unlocking all research.