........except for a turbocharger small enough it'd have to spin at over half a million rpm

Actually I think a supercharger might work on a 2 stroke given suitable port timing changes because one of the things needed anyway is a positive crankcase pressure. Our engines are already timed to match this positive pressure (and the inlet port is timed to match the negative pressure). Maybe it might only give better scavenging but even that would add some power. Whether the extra power is enough to drive the supercharger is another thing though .