I wonder about the same thing. I tried really hard to get BMW to supply my car on non RFTs, but they said they weren't allowed - something to do with deviating from standard spec.
I'd like to see what the car feels like with Michelin Pilot Super Sports on. Was thinking of splashing out in the spring. Does anyone know if non RFTs will go onto the standard rims? My summer rims are the 19" 403s.