why would someone non uchiha or non senju be stronger with boths DNA than a pure senju with sharingan, or a pure uchiha with senju DNA. Stupid logic. Danzo did it, he didn't become special. Rather he had some experimental failure.
I don't think Orochimaru is able to gain the Rinnegan, there are certain prerequisites. Thats may be another reason why he aimed so greatly to obtain Sasuke's body; eyes of the sage.