I think at this point, if Intel is going to be retarded about their naming (what else do you expect from a PC company?), I think Apple should just call the next PowerMac the G6. It is technically the Sixth Generation chip in the PowerMac line isn't it?
My reasons for keeping the name PowerMac G6:
1) This desktop is the most "powerful" computer Apple offers along all lines.
2) It is the most trusted and recognized name in the industry and non-industries.
3) It has "Mac" in the name already to go along with Steve's reasoning of changing the name of the PowerBook.