I didn't even connect the 12 cloud elite > Kinkaku + Ginkaku combat squad > Tobimara was a double agent.
on the possibility of teaching Orochi the technique, He ALSO must know the seal (The one that kept Madara around even though Edo Tensei is gone.) So after he died, when Third was versing the First and Second, he did the proper seal to stay around despite the technique being over and sometime in the battle slipped through the 4 sound ninjas barrier leaving a substitute behind. From there, he continued planning. Probably setting the wheels for the "Moons Eye Plan" into motion via Akatsuki.
Also, good theory on Sasuke Sarutobi. That whole thing never crossed my mind. Everyone assumes that the third coffin was the 4th hokage, but Orochi couldn't summon the 4th. The 4th was reaper death sealed into Naruto and the Fox after all. It very easily could have been Sasuke Sarutobi (Oh man, even the nickname "Tobi" comes from there)
In short it's going to come to this: If Kishi tries to spin some story making Obito Tobi, bad writer. If it's all over Rin, then he is no better than Stephanie Meyer
If he makes it anyone else (even not one of the totally plausible 2 explained above) and they simply somehow stole/possessed Obito's body, better. How good depends on what happens (That Sasuke theory above is brilliant as hell)