Well, to begin with I wouldn't consider something in the A500 style a "handheld".
Toss out the floppy drive and replace it with a compact-flash slot and perhaps some battery backup NVram and it might be interesting. Had the BoXeR been finished, that could have become such a thing, with today's FPGAs they could also bring a 68K CPU into the FPGA along with the AGA stuff they were doing, at low power and respectable performance.
Out of curiosity, are there any chances of porting UAE to the PSP? That could be one solution right there...
