I don't know what plans Chris has for the new Cobalt range but sincerely hope its something a little unique and not just a carbon copy of the normal M. I really like the idea of a bezel along the lines of your second image, especially with the sandwich dial design.
Maybe a white or silver dial and bezel in black might be a nice option?
Internal bezel, if any at all. While I like your interpretation, the real test is how an external bezel would look on the M case when viewed from the profile. My worry is how much height it would add, and hence start to look a bit clumsy.