There was a Wavespark 2 released in January with an almost completely different mechanic to the first game, so perhaps they could "borrow" that and turn it into Tiny Wings 2 The debate begins here.
I personally do not think there are any more things you can possibly add to tiny wings that would make it to a whole-nother app, unless you did in app-purchases. Seriously, the only things I can think of are: Rocket launchers Killing things Food Enemies Super fever mode Death from falling incorrectly
There's quite a lot of things that can be expanded in the game, as this flash game proves: http://www.kongregate.com/games/fexLabs/dillo-hills
I believe a sequel to Tiny Wings is indeed inevitable. Then again, such a small team has only so much time... I do thus believe it's already being worked on and that this has to be a most time consuming effort.
Very awesome game, though it doesn't run that well for me on my i7 iMac, for some reason. A little chuggy (no idea why...).