At present there are no plans for a refuelling probe. Yes, the E-3D has both a probe and a boom refuelling receptacle, but to put this on RJ would introduce further cost and delay - the aircraft are different in both structure and fuel system. That would mean Boeing designing the modification, someone fitting it, flight trials, reciever checks and then a training program roll out - all expensive.
So I doubt we'll see it anytime soon until George and HMT give us more cash - hang on is that a flying pig? But who knows the nickname of the RJ is the "Hog" after all!
For now we have to rely on NATO allies to provide Boom AAR (US, France, Netherlands, etc...). That said the E-3D crews have seen far more boom tanking in recent years than probe and drogue.
iRaven