Brainstorm: ultra fast programmable control loop

[b_force]

Just bumped into a discussion with someone.  (you know, late Saturday night brainstorm discussion)
Just out of curiosity, what would you do with an ultra fast programmable control loop with high res ADC feedback in and fast PWM out?
Mostly talking about practical solutions, like current sense for amplifiers, power supplies, audio related stuff etc, but I bet there are many more options.

So what are your ideas?

[Jeff_Birt]

'Ultra fast' compared to what? How fast does a control loop for a given application really need to run? If you are controlling the temperature of an oven for example reading the temp at 10kHz is a waster of time as the temperature will not change quickly enough to warrant that. Sounds like your trying to design a solution and then find the problem

[b_force]

Fast as in a few ns. Say 10 - 50ns

Like I said, just a brainstorm. We were just wondering were things could be improved 
The discussion started with something like that someone thought there wouldn't be any more improvements because faster is not needed.
I mean nowadays there are ucontrollers and DSP's everywhere, but are there fields where they still scream and yell to get more speed?
Specifically in control loops compensation loops.

Just curiosity.