I just stumbled across this thread and realized I could put something to rest.
I looked at my DSC's FSW PSW trace file from my 128i. There is a variable for axle direction.
The 135i rear axle direction IS different than 128i. I am not sure why, but the 135i (N54/N55 and N47D20 cars) will have "wert_01" selected with a data value of 0. The 128i gets "wert_02" with a data value of 1.
Another thing to note:
DO NOT code your DSC for a 135i vehicle order! Just change this one setting! The 135i has all sorts of other different parameters for its brakes and engine and slightly different CG due to heavier engine.
The 135i rear bearing is an "angular ball bearing" on realoem and the 128i uses a traditional "tone wheel". The sensors are different part numbers too. Zero clue why BMw did this, but it is what it is. Also no idea how Suprgnat didn't have to code.
Additional info 8/27: I coded my 128i to the 135i "direction" and received no errors. I think the setting is unused. I did not test the start assist roll back specifically, but I didn't notice anything pulling backward out of my driveway.
No coding is needed for this swap.