Some sources say Renault will concentrate on the ICE while RBR will take over the ERS side.
I dont think Renault will/can follow the Merc split turbo path for 2015. The new engine has been fired up on the dyno in july 2014 according to C.Abiteboul but R.Taffin says in different interviews between august and september that Renault is still working on the same 2014 architecture. However he adds that Renault will evaluate other solutions like the split turbo...
Newey
“Well in our case, obviously we have an engine partner in Renault and therefore the division is very clear. We make requests in terms of what we'd like from the engine architecture point of view and how that would best install in the chassis. Renault are able to accommodate some of those requests - some of them. Others they say no they can't do that in the time available or they don't believe it's the right thing to do anyway.”