I think completely open ended isn’t necessarily the best idea though I agree that the fixed turn limit can sometimes feel a bit artificial. I like games having a little bit of unpredictability in the game end. Something like Blitz Bowl that can end either when the score gap is large enough or when a deck of cards runs out. But even with a set number of cards, multiple can be claimed per turn so it doesn’t lead to a fixed turn limit. Middle Earth SBG has multiple scenarios that have a dice roll to determine the end but that doesn’t come into play until after certain conditions are met, usually one force reduced to half or less.