Hi There
No (at least, I imagine not). Why should it? you set your aperture and focus at the correct aperture just like any mirrorless camera with a 3rd party lens. Stop down metering is then a thing of the past. The EVF will gain up to the brightness you have set whatever the actual Exposure value.
all the best
You can use this to judge the differences in dimensions pretty clearly:
Compare camera dimensions side by side
The M9's 4way control and dial stands much more proud of the body than the new M components. The bodies shift as you toggle them in the top view overlay mode.
However, the overall size looks to be very very similar. I doubt it will make a substantive difference in feel and balance. (And it will be nice to have that control dial slimmed down and out of the way ... I have felt it obtrusive on the M9 since I got mine.)
The new, huge battery is a major plus. Frankly, I can't find anything about this new M that I don't like other than that I wish it were the same size as my M4-2. And that ain't gonna happen.
When I order it, it will help me finally slim down the amount of equipment in the closet once and for all. No more keeping an SLR around for occasional long lens or macro use. No more switching between APS-C and FF, and the tangle of lenses that are required to provide the FoV choices I want for both.
Unlike others, I do trust that Leica has put a good sensor in the M and don't really feel the need to worry about that. All I have to worry about, really, is paying for it ...