Actually what I'd like to have is a swipe-gesture interface that would be completely user-definable.

A mobile device is after all a personal device, no two people should be forced to use same gestures to operate their device. On startup there should be some sensible defaults set, but then everything should be personificable. There is some minimal tuning available in SFOS, for example turning off the foreground application closing by downswipe but that is not nearly enough.