I know this thread seems a bit dead after one month but anyways...
I'm currently planning in a 68000 replacement board based on a Coldfire 5206e or better, something QFP with 0.65mm pitch. That is difficult to solder, but not impossible.
The basic idea is:
A kind of accelerator with DRAM, Flash, IDE port.
The amiga would provide chip ram, and chipset in the right areas. Everything runing under an emulation layer.
I already got some ColFires.
And I'm thinking how I'm going to program the emulation.
But the good thing would be to make it in a kind of "do it yourself", with schematics, soft, pcb layout... (under the GPL of course !).
If you want something small, and 8 bit, I'd recommend a 68HC11, they are quite powerful and have frendly packages (PLCC) and useful periferials.
I think that an AVR is also a good idea, but you cannot expand the memory.
For quite a bit I considered using H8/300H, they have a somehow similar programming model than 68k, and are some more or less usable packages. They are 32 bit processors with 16M addressable memory. Quite cool.
I even wrote my own simulator and a ton of floating point routines for it. And also got uclinux working in the simulator, when the port was still in its infancy (2001 or 2002). kinda fun, I never got to buy the actual processors, but learned a lot about them.
Another cool line to work are the Hitachi SH-1 and SH-2. There are some QFP with acceptable pitch. those are 20 or so Mhz parts. RISC processors... I also wrote a simulator and some soft for it, like I did with the H8/300H.
If you want some ideas or some (limited) real experience, I have plenty of both to offer.
Anyway I'm pushing now this CF thing... lets see.
