"Nicholas C. Weaver"
I believe foundries offer this already.
Maybe Austin L could confirm if Xilinx are using this ?
In noise immunity topics, we've seen the point made that the CONFIG cells have significantly different, and better, noise immunity ( so config corruption is less likely than logic corruption).
Why ? Sure, more steps will be needed - but spacing ?
There would be a case for really pushing the Speed rules for LOGIC, but going for MAX Yield (ie slightly relaxed geometries) on the CONFIG cells (lots more of them, _and_ they are not 'picosecond paranoid' ). There would be some trade off on CONFIG time, and leakage Current in a variable threshold design.
I think this could be checked experimentally - drop Vcc, and LoadCLK, and plot Config verify fail Vcc/Freq curve. Then create a LOGIC fabric shifter, and do the same for it.
-jg