Oh and for ARM emulation of 68k, it's a nice idea but will wreck cycle accurency and lock-step.
Cycle-accuracy is shot with any accelerator anyway; that's pretty much the point. If you need accuracy, you pretty much just go with the built-in CPU.
Well I don't know what excites general tech nerds, except after the event, and it usually surprises me. But the thing that really impressed people about the Amiga when it came out was raytracing. I've read a paper about quite an impressive real-time raytracer (several frames per second) implemented in an FPGA that ran at alarmingly low clock speeds, so maybe something like that could do the trick. Texture mapping and shading has served the games industry well so far but it's not "the real deal" and maybe it stops being the most efficient solution at some level of detail.
I'd like to see a link for that. "Done in an FPGA" sounds like the crucial factor there, anyway - raytracing is
made for massive parallelization, and in an FPGA that's easy to do. On a general-purpose CPU, not so much.