the only one who can challenge an uchiha in real sense is orochimaru.
if he was born an uchiha then undoubtedly he would have been on the same level as an uchiha specifically uchiha madara who is the ultimate shinobi of all times.
they were perfect edos kabuto surpasses orochi in only the no. of summoned edos and to manipulate them and 2 loser hokages had full freedom to use any ability against hiruzen but hiruzen showed them that why he thhe strongest of first three hokages.
of course orochi would not try to attack...
sasuke is strnger than naruto right now and always has been.there is no way biju mode can defeat the might of sasukes susano capable of using amaterasu and it is quite sure he can get naruto with amaterasu.
no doubt rinnegan is extremely strong probably unmatchable but the only thing that is better than it is sharingan.sharingan has ultimate ninjutsu,ultimate genjutsu,ultimate eye jutsu(izanagi,izanami).neutrally when u see it is the sharingan that is the ultimate dojutsu.rinnegan stands no chance...
if sasuke manages to surpass itachi which he will for there is no need of orochimaru to be on sasuke's side against madara.i mean sasuke can only surpass itachi when he gets rinnegan and then against madara only he can win.