As a mechanical engineer, this sounds like it would work indeed! Possibly the bouncing we see in the trailer is caused by electromagnets to vary their strength or it's just the uneven surface of the sphere causing it.

The magnetic head idea makes sense (kind of like EVE from Wall-E), as it is pretty visible that the head is bouncing around on top of the astromech’s main ball.

I want one

I'm pretty sure these are the droids I've been looking for

...im actually in love with the Alitalia R2. I must have him.