Madara implies that Rinne Rebirth would have somehow given him a young body. Don't know if that would have worked, but if it would, then Madara likely would just have had Black Zetsu take over Obito sooner to perform the technique. Either way, Obito would have been pushed to absorb the Ten-Tails and eventually lost, so Rinne Rebirth is going to take effect at some point or another.
He summons gedo mazou and needs it for life support. He also comes back without eyes. But he still was a sensor so he gets by. Forces Zetsu to take over Obito after Obito use is up and rinnes himself. Grabs his Rinnegans and stomps.
Kabuto didn't bring back his youth as Madara was expecting to return in that form irrespective of the revival method. If Kabuto didn't do anything with his body then Madara would actually have his past strength intact.