I'm not sure if it's a limitation or just wasn't thought of yet - but I'd like to freelook without the Rift as well.
Lot's of games do it, most commonly known is probably the ArmA series which allows to freelook using a modifier key.
Since you aim with the mouse (or gamepad) and dive into that direction that means you're constantly faceplanting your mask into the ground if you want to see anything.
I almost feel nauseated by the constant need to look up and down (dive up again).
I'll be frank here: this is unacceptable and doesn't feel like diving at all. More like remote controlling a torpedo with a fixed camera on the top.
What I'd like to see:
1) Allow the player to swim into a desired direction and press a key to be able to freelook around while staying on the set course.
2) While using gamepad use the right analog stick for freelook
3) Open those axis so head trackers can feed data to it. This would enable TrackIR, Freetrack, FaceTrackNoIR etc.
4) eventually TrackIR could be supported natively
Actually I'm really surprised by this. Yes, the Rift will probably be neat - but there are and will be many others aside from Rift and currently it feels that gameplay is actually _limited_ for players not using the Rift although it's just a development kit and has so many issues that it's really no use getting one.
Search the forums. You will find a few thread about this subject already.