My 2 cents on this topic: Elder Scrolls Online tried this and failed hard. Sure leveling up is extremely fun. The quests are awesome and the customization you get is really nice. Once you hit veteran rank levels though your playstyle choices become severely limited. By that I don't mean the actual number of choices drop, but the number of effective choices drop significantly. If you don't play one of only a few accepted ways at end game you just won't get groups. Its why I don't play that MMO anymore.

FF14 is awesome the way it is. Don't change it anywhere near how the OP suggests.