They will probably cap it all for ilevel and character level. There is so much lv 50 content though, with varying degrees of difficulty, that I wonder what they will do with it all to keep it alive. There will probably be a "lv 50 dungeon roulette" and "lv 50 trial roulette" so that new players will always have someone to group with when they do story questlines. But what about coil, extremes, and crystal tower?

I figure a lot of the expansion updates will be handled similarly to "that other game", such as ilevel advancements and new jobs and races being compatible with old content even if it breaks the lore. (IE: Yuguri telling Au Ra characters "I can't show you my face because you wouldn't accept me" in the 2.2 questline.)

What the other game never handled well, however, was keeping low level content relevant. Once you were over the recommended level, you were ineligible for random queue. I really appreciate how FFXIV hasn't been abandoning it's older content (even if I hate losing abilities when level synced), so it will be interesting to see how they handle it. I can't think of any other MMO that has this approach.