Like Ediros says, bringing in psychic powers is going to affect gameplay. The player now being able to read the minds of NPCs during conversations or resort to telekinetic attacks? We have creatures with unusual attacks but most of them are still somewhat natural even if they are the result of convenient mutation, but with FOBOS we suddenly had Glowing Ones with radiation projecting attacks which continues into Fallout 3 (and sadly NV). Something could be said for cybernetic implants breaking with Fallout which I will not deny but adding in psionic powers available to the player does so completely. What probably be next is psyker masters who teach skills like combustion, healing etc. The chems that buff attributes were introduced to make up for a lack of spells (and I guess the surgery as well), and each of them come with their own consequences such as addiction. Hmm, perhaps cybernetic implants should have come at the cost of charisma, the more machine parts you have the more non human you become.