I think you'll find that you can't fit many RC motors in the grip of a G36. It's been awhile since I worked on rc cars, but last I checked the 540 size motor was still popular. It's pretty large in dia compared to an AEG motor. There are smaller brushless motors for the rc electric airplane crowd that I've been looking at, but they don't have the flats that are present on AEG motors so you'll be into making custom mounts for them as well as making the motor driving cct cooperate with an on-off trigger. I'm guessing you'll need a programmed acceleration profile for the motor to maintain synchronization with the armature.
I think you'll also quickly find the PV (load pressure x velocity) limit of your bushing materials. Exceed the PV limit of the gear teeth or the bushings and you'll have a runaway wear condition. I think high end gears might not be the weak point in your design, but you'll find out that AEG pistons aren't up to the task. Another early failure point will probably be the tappet plate. No metal tappet plates are available and the plastic ones aren't especially rugged.
Good luck making a hicap keep up with your rate of fire. Airsoft bb feeding solutions are not designed for ultra rates of fire. You will probably find yourself engineering your own bb feeding mechanism.
Want nearly free GBB gas?