Following up on the answers to Is there no crossover point where shutter speed overtakes flash duration? are there flashguns or strobes that allow the user to set a "sustain" period where the light is maintained at its peak level for up to, say, 1/500? Or any practical hacks to achieve this?
(The benefit of this would be, as suggested in that question, that one could "reverse high-speed sync" flashes to shutter speeds in the thousandths.)
I'm not aware of any, and even though I'm not an electrical engineer, I think I can state with reasonable confidence that there aren't any, and won't be in the near future. That's because flashes work by storing energy in a capacitor, and it's inherent that the energy released from a capacitor starts out with a high voltage and tapers off, just as you see in the flash power curves (e.g. here: Paul C. Buff, Flash Duration Explained. It surely would be possible for a flash to be made which held the voltage constant for a longer time, but the existing design is relatively straightforward. Adding the system you're looking for would add a lot of complication, and that seems unlikely for what is ultimately a very niche case — and a niche already partially addressed by existing solutions, as your previous question shows.
It's possible that future advances in newer capacitor types ("ultracapacitors!") will change this, but even then, I wouldn't count on flashes like this becoming available, because... still, niche use case.
