Yea, the "hammerhead" at the end of C is the only plan I know of. They're busy remodeling the existing Concourse C right now.
Somehow I don't see GMIA messing with the numbering scheme much. As Tom points out, it's been in the current format for at least 25 years now. The regulars are familiar with it, and I can't imagine it being all that confusing to visitors. It's a well signed, relatively easy to get around terminal, and there has been very little movement of airline gate locations.
I guess for the C gate extension they will have to renumber C, or maybe they will try to "fudge" with an LAX
style use of "A" as an appendix (ie gate 28, 28A, 29, 29A, etc)