I've seen it done in Presteigne 2006 and it made for an 'entertaining' watch. There was a loud clunk of the pinion gear engaging as the solenoid plunged it into the ring gear (not sure if it went via the chain though) and then a horrendous noise which sounded like a rapidly rising siren as the motor (very) quickly accelerated the bike. Unfortunately it didn't last long due to the rest of the bike not being strong enough to support the power. I believe the problem experienced was broken spoke(s).
Had this not caused its demise then I suspect overheating of the starter motor would have. These things are only designed for short service cycles before needing an extended period to cool down. Even with the ability to disengage entirely via the solenoid actuation, it still wouldn't be feasable. As I say though, it was fun to watch and have speed past (if not momentarily).