I get this feeling that Obito is going to change his mind once he learns why Kakashi killed Rin (which I suspect may have something to do with killing Kakashi and taking an eye back, maybe it records memories or something?) and then he'll end up trying to stop Madara also, who as we know now is practically SSJ4 Tank Madara. Maybe before Obito dies he'll give the key to Madara's demise to Naruto and Sasuke, who arrives just in time. Which given the current theme will have something to do with them being a pair and only Senju plus Uchiha could defeat a combined being like Madara.