What if Madara was never planning to be revived by the rinne tensei,
but instead he learned somekind of body takeover jutsu (like Oro's)
and was waiting for Obito to intake the juubi for the whole time to then strike
and take over Obito's body thus reviving Madara with control over the juubi
It is a possibility. Not Orochimaru's jutsu, but Madara clearly has backup plans for being able to control Obito. Here are a few possibilities, using clues we've seen from earlier in the manga:
Madara rebuilt Obito's body when it was crushed. We know he installed chakra rods into the body, and already attempted to use them to control Obito. It's possible that Madara implanted other things in Obito's body as well.
Obito's body is half Zetsu. It's possible that Madara could force Zetsu to split away from Obitos body, taking the Juubi with it (and leaving half of Obito to die).
It's possible that Madara can use powerful genjutsu to trap Obito and force him to transfer the juubi to Madara.
It's possible that, since Obito isn't really the Juubi or that Obito is trying to change himself, that Madara could use Izanami to trap Obito in a loop, and then steal the juubi from his defenseless body.
It's possible that Madara can use his sharingan to enter Obito's mind and forcefully release the seal (like Obito did to Kushina).
It's possible that Madara could sacrifice one of his eyes for Izanagi, to undo his death and bring himself back to life. Then, he could "steal" back that eye from Obito to give himself 2 again (we know Madara has Hashirama's power, and we know Hashirama's power can radically improve the effects of Izanagi).
It's possible that Madara has the ability to use Creation Of All Things, and can forcefully build himself a new living body out of his chakra. If he can use chakra rods in Obito to steal the chakra of the Juubi, he can then use his new body to seal the Juubi away from Obito.
There is another Rinnegan in Obito's hideout. One of the remaining Zetsu clones can gather that eye, and use it to bring Madara back to life.
Madara may know some other technique, Rinne Tensei or similar, to allow him to bring himself back to life without Obito.
There are lots of options here. We don't know what Madara is thinking yet.
