Dear Roger,
"A lot more" might indeed be an exaggeration, but I like to think there are people out there with ideas bigger than mine and a drive to see them come to life...I also believe that in 2010 (today) we can fit (some) additional technology in a 1950s body's dimensions.
As you have noted yourself there are too many variables as to what constitutes an improvement based on each person's experiences and preferences, for example: Is AE good or bad? Small or big shutter dial?
Well, here are a few things I know of (I'm by no means a reference) that exist already and that I think would improve user experience (the ones I consider important are bolded):
+variable magnification viewfinder depending on the mounted lens (Contax G, Canon)
+single framelines (Contax G, Canon, ZI)
+big eyeglass-wearer friendly viewfinder, ie. Let me see 35mm frames with my glasses on! (ZI, at .74 and not .58)
+field of view compensating framelines (Konica iiia)
+film canister window (would save the M7 the 2second boot-up sequence and frustration with the film speed reader)
+easy exposure compensation dial (ZI, Contax, Bessa, Hexar, CL/CLE)
+easy AE lock (these last two points seem to be a direct result of using a body made in the age of non-electronics and trying to fit new features in a body not made for it)
I'm leaving things out that I don't necessarily care for (auto load/wind —I actually like loading my M2—, high flash synch/top shutter speed, flash sockets not poking left-eyed shooters in the forehead, autofocus with manual override, ect...) or duplicates (backlight compensation switch as in the Contax G and Contax T would be a sub category of exposure compensation).
The improvement I can see?
+LED assisted framelines when in the dark
+focus distance indicators / dof
I have a feeling Leica has exploited all there is from this M body shape. Some idiosyncrasies of the M7 seems to indicate that, and the full loop back to the origin with the MP might be a confirmation of that feeling...But, I'd love to be proven wrong with the next film M (or something really new?) release...