Is this the idea of the stepped flywheel/stepped trigger spacing as you mentioned here: Simple, proven, off-the-shelf industrial V-twin? ? It seems like a clever approach, but possibly fiddly (to get the spacing right). It also seems unlikely that both cylinders would make the "hop" to the new timing at the same time.Briggs coil with large air gap (could be around 8-10deg over rpm range, might need stronger magnet)
I guess there's no practical way to have multiple selectable trigger coils per primary magneto, or to electronically delay the triggering of the main spark impulse.