This is not a who is Madara I honestly think he is the REAL Madara rather what is Madara.
I think Madara has become like a Zetsu like creature due to his exposure to Harashimas DNA.
In exactly 4:03 when Madara drops his arm It can be seen that its not blood but rather a white substance (similar to white zetsu's body) coming out of the injury ,many off you may think oh thats just the poison from the bugs but keep in mind the beetles didnt act that fast when it touched Torune. Also Madara arm "magically" grew back soon after this fight suggesting that he really did grow it back.
I think after all the experimenting with Harashimas cells he transformed his body to have like a zetsu-like physiology enabling him to regrow his limbs and live longer. He may have also created Zetsu from Harashima's cells seeing as how Zetsu seems like the only person to not have any motive for joining the Akatsuki besides following Madara(because he is his creator).