Do not force level caps on content - You segregate the player base

[Andrien]

And then everyone who is level 50 has fk all to do.

I don't think you thought this through. I doubt the dev team will leave that wide of a level gap with nothing to do. It is safe to assume in this scenario there will be content that has requirements for 50+. Besides 50s attempting something that is meant for 60s is something a leecher would try to do anyways.

Players will be gaining experience point while completing the main story, and questing in xiv, so I really doubt they'll implement caps for that, especially if the quest are all level and party difficulty appropriate.