That's what I thought Drizzt321 ... and if the focal plane shutter isn't being used we can sync at any speed !
Mirror would need to be locked up (or live view used), but i think it might work without compromising flash reach / distance !
If your subject was moving so slowly that you could shoot it with the mirror locked up, why would you need a high speed shutter?
Erm...it's not that the subject is moving so slowly, is that you want to use a high shutter speed with a strobe/speedlite. Traditionally you were limited to the shutter sync speed or use high-speed sync. But high-speed sync generally (at least with standard Canon ETTL speedlites) reduces the power output substantially. If you want full power, you generally need a whole bunch of speedlites together, or some types of studio lighting.
If you remove the physical shutter from the equation, you basically have the entire sensor exposed all at once, then it's however long the electronic 'shutter' is that determines your sync speed. So you can sync at, say, 1/4000s at full flash power. Can be quite helpful to balance back lit subjects with fill flash, but having that fill-flash be at higher power to balance correctly with the back lighting.