I have a deposit on a 135i. In the thin air of Denver a n/a engine like M3's loses over 20% of its power & torque while turbo motor of 135i loses none (with a bit additional lag). Cheap tuning (under $2k) is available for 400hp and 400ft-lbs which is WAY more than M3 power and torque at altitude and the 1er is lighter. You can buy a Quaife LSD for the 135i for around $1,500 plus install (yes, electronic solutions to LSD suck!).
I also hear that there will need to be additional oil cooling for the 3L TT motor (335's are overheating even in stock configuration). My understanding is that with proper oil cooling, the 3L TT motor should be able to sustain the tuned output (400hp/400 ft-lbs), but these are new cars - we'll have to see.
But even totally stock in Denver, a 135i will be faster (in a straight line) than an E92 M3 (300hp and 320ft-lbs @ 1,400rpm and 3,250 lbs weight for 135i vs 325hp and 240 ft-lbs @ 5,000 rpm with 3,500 lbs for M3) and cost only 60% as much.
Although Kreso has assured me my worries are unfounded, all of my additional research shows that the 135i will have electric power steering though (please see .pdf attachment above of German dealer sheet which I believe shows electric PS for all 1er models - please correct me if my reading of the German is wrong).