Atari 600/800 XL is up next... I don't have Atari 800 which would make it easier (hardware wise, that is... don't know if software needs to be patched for 65C802).
I think the 65C802 will work in a Commodore VIC-20 since it used the originally MOS 6502, and as far as I know both these chips are bus compatible - that's the first thing I will try as soon as I got my hands of that elusive 65C802 chip anyway :-)
I will try to make a drop-in replacement for the W65C802 chip but need a few samples of the "real thing" to reverse engineering it, so I'm definitely want to buy it! will send you a PM right now!