Yeah I mean 360 and PS3 are fairly equal in terms of graphical powers (PS3 being a bitch to code for and it's cell processors being wasted on daft stuff knocking it back a bit unfortunately). I reckon it'll run just fine on 360, didn't see anything in the limited gameplay footage that was uber amazing in terms of graphics.
The difference is a bit bigger than you think. Is it enough to affect XIV? No clue. But, when a game is made to take advantage of the PS3's power as much as possible, its Xbox 360 counterpart will be more than noticeable.
But, remember, graphics are only one consideration, and likely not even the greatest. Even if the system is fine as far as power goes, there may be many more issues.
For example, how does the XBox Live connection compare to PSN?
How does the fact that XBox Live isn't free as the PSN influence it? Maybe none, maybe a little.
How does SE feel about the red ring of death? Does this mean they need to put in some kind of delay mechanism for payments? Will the 360 customers have to pay for their services for the 2-3 weeks they don't have the game?
Will PlayOnline or similar be used (oh God I hope not)?
Is the game going to have its own Voice channels, or will you have to connect independently of it?
And then all the REALLY important business stuff, like money, promotions, advertising, market, economy, etc.
Remember, the porting is only worth it if enough people will buy it on the 360. One would assume that players that have both systems will play it on their PS3 or PC. So, the question is whether or not enough gamers that would go for it exist that would not play it on the PC, but would on the 360.
With a game like FFXIII, the decision to port it was natural, as it wasn't on the PC as well. But, that changes things a LOT for XIV.