It takes longer than 6 hours? All you have to do is pause and charge the game or just play with the charger attached??? It seems way easier to tackle a 50 million HP boss with a handheld than something attached to a TV because you can take a break and resume whenever/wherever you want instead of damaging your eyes or pissing off your family for hogging the TV. Since FFXII is mostly moving the analog stick and not pressing buttons (gambits), you could probably eat lunch while fighting it too.
Anyway I don't see why there shouldn't be a Vita option, and am hoping to see one when it is announced.