What's the technical challenge here? Is it more of a marketing decision to encourage you to pay more for TTL based models (let's disregard other advantages of TTL for the moment). If we can have flash with high enough burst frequency we should be able to fill the frame regardless of the shutter speed or 'slit height' right? Feel free to go as technical as you need, I can handle that. Thanks in advance.
The problem that is solved via high speed sync has nothing to do with the power of the flash and everything to do with the curtain transit time of the camera. Above a camera's sync speed the second curtain begins to close before the first curtain is completely open. Therefore very precisely timed multiple flashes must be emitted from the flash as the open slit between the two curtains moves across the film/sensor plane. Manual flashes are not capable of this precision because they are not capable of two way communication between the camera and flash. The are only capable of receiving a single command to fire.
HSS requires the pulses from the flash to be timed to the particular shutter speed selected and must also take the camera's shutter transit time into account. Transit times and sync speeds vary from one camera to the next. Even if the flash could be manually set to the shutter speed selected in the camera, how would a manual flash with only a fire communication capability know the precise shutter transit time and thus be able to calculate the timing of the pulses needed? Then there's even the issue that one camera's 1/500 second may actually be 1/478 second and another camera's may be 1/511 second.
Godox has several lines of flashes (everything from speed lights to studio strobes) that are manual with HSS. The challenge is HSS requires the trigger interface with the cameras proprietary flash protocols and so if you're doing all that you might as well do TTL. Godox gets around this by making HSS an off-camera only function. So the flash has a single firing pin but if if you use the right radio trigger the flashes will utilize HSS with a variety of cameras.
Back in the day I had a camera that selected between Flash bulb and the then new electronic flash. The Flash bulb didn't have a brain nob did it need to communicate with the camera. It was that the Bulb would be instructed to fire as the first curtain began its travel and would burn longer covering the duration of the exposure.
The original question is still valid. If the flash is set to have a specific duration of 1/250 second then it is only a matter of timing the initial start of the burst.