TTL Flash for Mirrorless

"FP operation is not continuous, but pulsed at a high rate (240 fps?). That was sufficient for older cameras, like the Leica M2 and M3, which had a traverse time on the order of 1/50 second. Shutters which traverse at 4 or 5 times that speed are likely to produce inconsistent or banded results with an FP flash mode."

- Ed, you're conflating FP shutter synch with HSS mode on a flashgun. They're not the same.

FP shutter synch simply sets the flash to trigger as soon as the first blind begins its travel, it cares not what the flash output is like. HSS is purely a function of the flash, and, as you say, entails the flash being rapidly pulsed to extend its duration.

Thus:

As you can see, at full output the flash doesn't 'flicker' at all, and yet remains fully useable for the duration of the shutter travel. There's nothing to strobe with the shutter slit, but the flash illumination isn't totally consistent across the frame. However this usually isn't noticeable, or even important if the flash is being used to fill daylight.

FP synch could be easily manually switched on or off in any camera that offers HSS, and would be a very useful feature to those that know how to use it. The fact that it's crippled and can only be set by fitting a compatible speedlight shows that camera makers are far more interested in selling expensive accessories than in providing useful features.

BTW. You can also see from the above curves, that the peak illumination provided by a flash in HSS mode is a fraction of that at full power. Making it even less useful as a daylight fill.