i was already thinking before that tobi might not be an uchiha, and that theory has gotten stronger the past two chapters. the only idea i had before that tobi is someone who isnt an uchiha but has a high amount of chakra like naruto. thats why he wore a mask concealing one of his sharingan eyes so that the amount of chakra drained from him will be cut in half, similar to why kakashi covers his sharingan eye when he doesnt need it. now its more and more possible given the fact that if tobi could have simply awakened his rinegan, then there would be no need to take them from nagato. although kakashi was still able to upgrade the two tomoe sharingan he got from obito all the way to a magenkyo sharingan.
leading candidate right now is still madara's brother to be tobi because clearly its someone he knows. but im curious on who else could be the one behind the mask that knows madara personally, know that a jinchuruki's seal is at its weakest when she's in child birth, and still realistically be alive till now. i also want to rule out every single person thats been summoned so that takes away all the previous hokages. it makes me wonder though why kabuto hasnt revived orochimaru yet. im sure he's had enough blood sample from the past.