It is totally possible to build a "self-righting" bike, I've done it before, but for less than noble reasons...more just because we were bored and wanted to see how it would work. The design has to incorporate negative trail though and you would need to do something like having multiple forks to change the trail/rake as the rider gets better. I'm not sure if that's exactly what your after, but with a negative trail set-up, the bike will actually stand itself up as it starts to lean over. You literally have to steer it into the ground.