The R's appeal is the AWD period which you won't get with any other performance Golf, it's certainly not the sharp looks or focused character.
I wonder, what if VW matched BMW and said you can just add AWD to any model for $$$$$$...
Of course its technically possible, these cars are fully modular.
Golf 1.1 Match AWD 
Completely off-topic but hey...
The thing here is, BMW has a much more extended model range (say of the 3-series) that can satisfy different power needs (320i, 330i, 340i, 320d, 330d, 335d) and yet keep (at worst) a safe 100+bhp deficit compared to the series flagship, so offering AWD is not threatening any M3 or M4 (funnily those aren't even AWD, at least yet!), let alone all the differences in setup and dynamics.
Looking at the Golfs, the first version which confidently steps into the performance class is the GTI. 65bhp and a mere 20Nm down from a R while dynamically - although there are differences - there is not much between them and if anything, the Clubsport was actually a better drive than both. So If a GTI AWD existed, I bet several owners would see the jump to a R un-necessary and for that I don't think it's going to happen soon. Then again, at the pace bhp is increasing currently, AWD will be a necessity sooner or later. If/When that happens, WV would have to differentiate the R a lot more (styling and drive-wise) to keep its flagship status intact.
