I would be all for swimming in limitedly locations, Or with a special buff or something..
That or take your gear off, so it is done diffidently and with a bit of a challenge or something not just a way to move around freely like most mmos.
Stripping down to swim around in deep caves or special gear would be a cool way to do a instanced area for hidden rooms and Forgotten citys and stuff..
Or maybe we need a plant to breath though and we can only use it for so long an so often as its poinsonus but then we can walk around under water and climb cliffs if we want to keep gear on?
I dunno just something different..
As for Jump FFXIII style imo, or again in limited situations.. The way of the bunny is strong in MMO players and it take a lot of of the PvP (more then it adds imo at least)