Your characters "starting budget", accumulated money/credits and available tech dictates what you can get for bionics/cybernetics in Rifts, but that would even make sense in the Fallout universe. We have the BOS, the Institute, and to tap other sources like the Fallout 3 DLC Old World Blues, or even the aliens in the Fallout universe, I'm sure it would be possible to create a boinics/cybernetics system for FO4 that stays lore friendly... Edit: I am actually surprised no one has really done cyberpunk properly in the Fallout universe before - it kind of makes sense in that universe.