Unfortunately, there's another problem with the current-generation programmable logic in which one would most likely be tempted to generate the memory-mapped i/o to which you refer, namely the i/o voltage at which they operate.

It's pretty difficult to get useful work from a CPLD, for example, when its I/O voltages are limited to 2 volts or less. Only recently have I found mosfets that can be driven with such low voltages, and, if one adds level-shifting buffers to a programmable part, it often quadruples the cost. Bidirectional I/O is really interesting.

Careful consideration of precise I/O requirements is needed nowadays. 805x-compatibles also seem to be wandering in to the low-voltage domain, probably for just exactly the reason that logic no longer tolerates 4-5-volt levels, which are pretty much the minimum at which one can effectively control external hardware devices such as solenoids, relays and motors.

RE