In the FINAL FANTASY XIV Letter from the Producer LIVE Part III video there is a part were they talk about direct X (not the point of this thread) what is talked about during this question is.
Link: http://www.youtube.com/watch?v=TnFLSH2jkjw&t=35m17s
". . . After launch, our next big milestone is DX11 compatibility. Once we achieve this, there will be a further improvement in graphics. . ."
". . . Technical Director [Yoshihisa] Hashimoto was recently talking to me about whether it's possible to further increase graphics quality on the PC version, so we need to decide how ambitious we want to be. . ."
First this will quell some thoughts on graphics, as we can be certain from alpha to beta to launch there will be at least some graphic changes (specially water, hair, lightning). But even after that we (with good enough PC) may see an even better increase. That they have plans to continue even after release, this is good news.
I just want to say please let Yoshihisa, let the engine dig deep for those PCs that can handle it (and players who cant, can still play this game for years and when they buy a new pc they will have -a lot- to look forward to).
Longer graphic shelf life as PCs get stronger.