"I wonder if someone could design a flash unit that worked like a FP
bulb? Wouldn't that give us flash at any speed?"
The F280 is such a flash, but it works only with Olympus cameras. There
are several reasons why it's unlikely we'll see a "generic" flash of
that type that would work with other cameras.
First, there are (I assume) unexpired patents on multi-burst flashes.
Second, this sort of flash is wasteful. Every time you halve the shutter
speed you have to double the flash output. You would need a much larger
flash tube and power supply.
The most-significant reason, though, is that an "FP" electronic flash
isn't very useful. Why? Because it would be difficult to build an
auto-exposure system for it. Here's why.
If you open a shutter all the way (in either leaf or FP), you can then
fire the flash and integrate the reflected light until the correct
exposure has been reached, then close the shutter. This works for both
electronic and chemical flash. (The Polaroid ColorPack cameras used it
for flash bulbs.)
But... when the shutter can't be opened "all the way" (as when shooting
at FP speeds higher than X-synch speeds), the correct exposure has to be
determined _before_ the flash even begins firing!
How can this be done? Well, if the camera knows the distance to the
subject, and the camera has direct control of the aperture, it can set
the correct aperture. But no professional photographer would be happy
with such a system, as it lacks control.
Another way would be to fire a brief pre-flash to determine the correct
exposure. This is workable, but decidedly "clunky."
In short, don't hold your breath waiting for such a flash. Several 35mm
SLRs have X synch at 1/250, so it's unlikely manufacturers will be
designing electronic flashes that can be used at higher speeds -- it
would be easier to gradually upgrade the shutters in your product line.
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