You're right, this wouldn't work with the current ac.scm. However, if we stop treating the symbol 'nil specially and just let it be a normal variable lookup, then I think everything will work.
The only hard bit, actually, will be making it output things using 'nil instead of '(), but making a fix like that, that's isolated in one small part of the program, seems like a small price to pay for making the main arc compiler sleeker and faster (oh, and the generated code, too).