It worked in WoW, although I hate mobs that level up with you it removed the progression feel of your character getting stronger. If they do it they need to do it in a different way where the feeling of progression is still there.

In ffxiv I am not sure how it works. In WoW the story for each expansion is sorta a stand alone story, some minor ties ins but mainly standalone. IN FFXIV the story is highly linear and the expansions are sorta a continuation of the story, letting someone say skip heavenward or ARR would be like coming in on series 2 episode 8 of a on a tv show and saying ok whats going on now.

This is an issue of progression in general in a Themepark Game. I think they need to cap the levels and add other forms of progression. Why games with horizontal progression do not have the issue. But to keep ffxiv pure linear, they could cap the lvl but with the current gearing system it would be no different as you would be say lvl 80 in Ilvl 10000 gear doing 1million dps with 5million health. I do not see an easy solution for ffxiv. Horizontal Growth is the answer but the game is pure linear and I do not think a redesign would be worth it at this point in the games life.