I saw in a German magazine "Amiga Magazin" issue 1/97" an expansion to transform an A500 to a fully blown A1200.
It has Kickstart 3.1, AGA Chipset, 68020@14 Mhz processor and a Expansion slot to expand it with faster accelator cards. It called AGAGo.
Here you can find a small picture of it:
http://www.amiga-magazin.de/magazin/a01-97/messe.html
