I guess you haven't seen Losi's LST XXL2 and 8ight series buggies and truggies with the .31 gas 2 stroke engine (same footprint as a nitro big block) with a CDI powered off the 2s lipo also used for the receiver. I forget the exact max rpm quoted by the Losi rep on another forum but it was right around 30k rpm for that engine and the CDI box is about the size of (likely a bit smaller than) one of those old school 4 AA battery holders. I can't say with any certainty but no indication was given that the CDI box couldn't handle more rpm, I believe there was no reason to spin the engine package faster as it wouldn't make any more power.

I agree with quicksport about the benefits of converting to a spark plug. I also think starting with an engine like this already intended for gas offers some benefits. Instead of varying nitro content and dealing with glow plug heat ranges you could just up the octane of the gas used in the premix to ward off detonation. Or if you wanted to go further you could alter the flywheel to accept a new key way to retard the ignition timing, probably easier than machining a new head with more chamber volume, although adding head shims would be even easier.