Tbh, the first thing that comes to my mind is about : "All is needed is a left/right/up/down and space/ctrl key simulation.".
I'm afraid this is not true.
I mean, it really depends on the game. A simple game with two actions, sure this will be enough, but on a game using more keys, or using only the mouse plugin (instead of/not having a touch with "use mouse input: yes") I'm afraid your idea isn't as effective in those cases.
I'm maybe missing some big picture there, but it seems to me that it should be the game's author responsability to make its game accessible to mobile devices, not an "after-thought" patch.
Also I don't know if, technicaly, a plugin could cover all cases.