I'm going to find one of these M135i motors and have a drive ASAP.
I don't think they're available until September so not sure when we will see the first ones.
Having just placed an order for the M125i yes you would be looking at September if you placed an order now.
As I've been more than happy with performance of the GTI I've not really considered the 135 tbo. My GTI isn't mapped either ( I'm one of the few on here where that doesn't really fuss me ).
As my car is a daily commuter the fuel and tax costs would kill me on the 135. Also opting to buy the 125 which is 3-4 grand cheaper has allowed me to spec the car with plenty of options