I've been thinking about doing this to an old A1000 I got as a freebie. But I think I'm going to wait till the A1-lite shows up. .. keep it in the family, eh? :-)
The catweasel sounds like the best approach. I would probably go with the dremel & bondo approach to fit the guts from a pc keyboard into the 500's case. On Aminet there's a project to build a pic-based translator to connect a pc keyboard to the amiga...