[sparoz]

Let's look at it this way - if we are in BMW's shoes -
a) It needs to convey it is a M, ie M needs to be in there and in a way that people won't think it's not a true M.
b) It needs to convey the series where it comes from and it doesn't cause confusion.
c) ///M1 is ruled out

Although ///M Turbo, ///M Coupe are good names and they had previously used one of it before, it doesn't convey 'b'.

Which leaves 1///M a possible still as they have to have x5///M for obvious reason, and they can easily to do it for the 1.

The only other option would be to use the internal code ///M E82 which would be confusion, or add something else to ///M1 to distinguish from it from the old car like ///Ms1, ///M1s, ///Mt1, ///M tii 1.

///M2 is possible if they are going to rebadge the 1er Coupe into a 2 - but that would cause more confusion.

I still think calling it the "1 series ///M" as the official name, and with just a ///M badge still is a possible option. But 1///M could possibly be the strongest and easiest to explain.