You'd have to be careful about the ARM core; arm are very protective (look at what happened with PicoTurbo).

You'd also be hard pressed to get anything of the performance of a StrongARM out of even the very expensive FPGAs. I suspect that doing it with off-the-shelf chips will be cheaper in terms of design time and component cost - eg, replicating the ADCs/DACs/etc with a digital FPGA isn't going to be easy.

FPGAs are great for lots of things, but for shrinking a fast CPU with lots of cache (24k) plus lots of analogue I/O I would suspect you'd be barking up the wrong tree.

Hugo