For me the M11M images have much better tonality and a special character to them that I do not remember the M10M images as having.Probably not a provocation.
I am moving from M10M to M11M, not for image improvement which will likely be indistinguishable from M10M but for things like better battery life, commonality with M11, better EVF, electronic shutter (ND's no longer routinely needed), superior Leica Fotos integration). There is no need for any of this, heck, there isn't even a need for a monochrome camera or a Leica... but its a choice.
I never owned a 246 but I can't believe you are in the least bit handicapped in the world of monochrome imaging.
Plus all the added benefits of an M11 chassis