well it doesn't specify how much senju dna is required. and if the senju and uzumaki are one in the same, wouldn't nagato have it regardless? i believe it was given to nagato because there clearly isn't any other person with senju dna to give it to( not tsunade or nawaki) and if madara already had senju dna....maybe it isn't pure...? im starting to think that this could be possible. maybe hashi and his motley crew weren't the purely senju? both senju and uzumaki have strong life force, and it is only shown that nagato(uzumaki) achieved rinnegans full capabilities. maybe the senju really are the off shoot, and we are being redirected? the sharingan can control tailed beast, the uzumaki body can sustain their capture... the senju could be to the uzumaki, what the hyuuga are to the uchiha.