the tobi obito theiory had to may holes in it earlyer on in the sieries to holed up to anything but from what weve seen in the bast few months it could be posible for obitos body to be used but the fact is obito died in gaiden but that is about the same time that mandara was supost to have used the kyyubi on konoha so maybe it fills in some holes as to why mandara isnt dead why obitos body is alive and how mandara summoned the kyyubbi, maybe the sharingan is tied into the whole thing and mandara just needed a vessel to seek his revenge.

my theorie on why he didnt return sooner is just simply that obito was crushed his sharingan couldnt have survived and no hunternin was shown disposing f him so maybe the fourth overlooked this due to that damage and mandara somehow retrived or enterd his body to claim the sharingan and maybe the whole itachi killing his cn was a test of his sharingans power wich mandara is intrested in to see if he if he was a sutable host or what ever for mandaras power.(obito was weak so he wouldnt have had asmuch skill as an uchiha as say itachi and the clans founder)but now as we see tobis interested in sasuke and itachi wants to tell sasuke something more important that capturing the ninetails.