I think after 8.0 they could probably put Shadowbringers and Endwalker in the free trial, so people can experience that whole story at their leisure without a subscription. Then I don't think there would be a need for a new start point really, but I suppose since the story is just going to get longer and longer they may want to do something to get people out of the free trial and into paying faster. If they do make one, ideally they would make a "previously on" style cutscene that shows a reduced version of all the story being skipped when someone starts at the later start point.

People who want to skip just to get to endgame ASAP seem like a different issue, I would hope anyone with that mentality also wants to be good at the game and is going to engage with systems like Stone Sky Sea anyway. I don't think they need a new start point since the skips already get updated every expansion to get you to the start of everything new.