For me most used lenses on M8 were 28 and 50, followed by 75 and wate.With my M8 at least 95% of the images I made were with a CV 28/3.5. If I were buying one lens for the M9, therefore, it would be a 35 - either a Summicron or a Summarit depending on how rich I was feeling.
A 2-lens set would probably be 35 and 50.
A 3-lens set would be 21, 35 and 50.
I actually have 15, 21, 28, 35, 50, 65(Visoflex) and 90... All of them CV apart from the 65mm Elmar. However I understand from Sean Reid that the 15 is 'problematic' on the M9, so only time will tell if that line-up is likely to last - I've rarely used either the 65 or 90 with the M8.
This would translate in 35 and 75 and maybe 21 or wate.
However from first feel 50 now seems pretty attractive focal length as well.