If they just call it the "1 series ///M", and not to use the ///M1 badge - that would be fine. In a marketing perspective, I think the car will need to have ///M badge, and without the '35', lets try some of these.
Joy is indulgence - the BMW 1 series ///M
Joy is indulgence - the new BMW ///M Coupe
Joy is indulgence - the BMW ///M2
Joy is indulgence - the BMW E82 ///M
All of the above will only have a ///M badge except for the M2. I feel that although M2 will work, it is probably not their option as the 4 and 6 are niche products despite the 1er Coupe was supposed to be a 2 series and Scott did say they won't be using 2 for the current lineup.
Seriously, I actually think they might just market it as the 1 series ///M, with ///M badge on the car and no other numbers.
Of course, if you going to have a 1series MDrive - that would just be stupid.