The official response from VW seems to be along the lines that the EA888/ K03 combination cannot reliably produce the power they needed for the Nurburgring 24 Endurance. Hence they installed the 2.5 5 pot in the race car.
This statement plus the apparent installation of the old K04 configuration presents a very strong case that the EA888 engine is not actually suitable for running big power.
But I smell what could be a rat...
The Mk6 is (all jibes aside) a re-designed Mk5 which was released with the aim of cutting the production costs of the Golf. With the 2012 scheduled release of the Mk 7, I am suspicious of VW's claims that the EA888 cannot reliably handle an extra 30bhp. Personally I think it is cheaper for them to run out a bunch more "old" engines rather than manufacture the EA888 in a new configuration. Lending support to my thought is the fact that plenty of K04 powered engines are being run out for the Scirocco R, Golf R, S3, Cupra and Cupra R, so it's not too difficult to simply add a few more engines to the production line rather than creating a new production line.
VW being the company that it is, I think they would have noticed before they made the Mk6 whether or not the EA888 could handle 210 bhp (and the usual headroom built into the engine).
I've heard it said before that the engine isnt up to the job but many guys here are running much higer HP than 235 on their MK6 engines. I know that Volkswagen Racing limit their ECU BHP increase to 250, although they say that's to do with optimal power for the car than the ability for the engine to handle it.
Bigger and better people on this forums know more than I do so no doubt they can help further.
Jim
I'm neither bigger nor better but I have been running approx. 265 hp on my mk6 for the last year and a half with no engine problems.