If the kill itself rewards something gainable indeed. if you have already gained something, the kill probably would be worth nothing (extrinsically).
Dropped loot may also not mean much to lets say a purist PvPer… However that is not to say that intrinsic motivation would be decreased… Games like counterstrike thrived off pure instrinsic motivation for a long time ‘i beat you, and that increased my dopamine levels… mofo’. That is not to say that it wouldnt be possible in Orbus… But… You can see that the original counterstrike evolved in to providing custom skins (an extrinsic reward) to players etc… as did many other PvP based games.