Everything in the car is already in production in the VAG range, bar the engine which is going into production on the TTRS. It is an R with a bigger engine.
I was under the impression that VW would be using a heavily modified version of the 2.0l that's currently in both the GTI and R. There was no suggestion that the R will get the 2.5l engine that's in the current TTRS and which is also likely to be in the new RS
Apologies, meant the TT Quattro sport 420
This uses the EA888 2.0 and not the RS 2.5 engine, could quattro GmbH be dropping the 2.5 engine in favor of the more frugal and lighter EA888 block?

This also means that there is still more room for performance out of the Golf R400... another 20bhp can be had... but this will probably be for the Audi RS3 / TTRS... 420/430bhp perhaps?
it could happen as EU guidelines get trighter on Co2 emissions etc.