ste-phan, there's an application for the N9 (My Moves) that gives you a dozen or so additional gestures and lets you define actions for those. In principle the programm is designed so that one gesture starts another application (boooring), but with dbus and shell scripting I was able to define a gesture that calls a certain number instead of just launching the telephone application.

Now in principle, if (and only if) an application like the browser exposes certain features to be controlled via scripting from the outside world, all it would take is "My Moves" to be ported to sailfish and you'd have your very personal additional gestures.

(I know there's two big ifs there... but it's better to approach it from this side, I think, than to break the whole UI concept.)