Depends on how it's done I suppose... WoW did it to the worst end. Negated past content with the implementation of easier content. If you break it up into the various level caps... 60, 70, 80... once you raised it, content @ 60, for example, became obsolete and noone ran it to any large degree. Thus people get to level 70 without learning everything possible from level 70. Cycle continues until naturally you're adding all the new content with the same span of difficulty. Never really building on this, and there is no real sense of progression, but leap frogs of content.
Personally, my preference lies in something similar to Monster Hunter. Levels and Ranks become meaningless, and there is just challenge after challenge after challenge, each requiring gear/skills obtained from the previous. Otherwise FFXIV will become like WoW, where you grind dungeons for a year to get all the best gear, then they implement a level increases that destroys the value of the gear you spent large amounts of time obtaining, just to go and repeat the process.
Honestly, I feel this is a terrible idea, and I hope they would be careful not to follow WoW's formula.