Honestly I dont see how the M1 can be all that better (performance wise) vs a properly moded 135i.
M suspension => we got it. Swap the pieces from a M3
Power => LOL
Brakes => eheh , some holes on the disk wont do sh!t, change your pards for something better and thats it. Want to get fancy, get a 2 piece rotor
The only you wont have is the M status and 20k less on your pocket.
Well, probably the interior will be more "sporty" But even that you can buy it if is what you want.
The only thing I whould love from it is the roof and hood. Possibly the trunk. But since is the same chassis well.
Hopefully there will not be HPFP misshaps.