As far as we all know Edo Tensai cannot be released by anyone other then the caster and if this is the case something is really screwy.
Sure S06P summoned the past kages to help with the summoning jutsu but it was not him that summoned Hashirama, Tobirama, Hiruzen and Minato it was orochimaru. So why is it that when So6P released the pure summoning it also realeased the 4 kages. Im leaning towards maybe orochimaru has been turned into a zetsu but if thats the case then the kages wouldnt have been freed of the edo tensai.
I also thought of the same thing, that is Orochimaru is turned into Zetsu. However, even if he were turned into zetsu, the principle of edo tensei says that
defeating the opponent cannot even stop the Jutsus. In my opinion, there are two possible explanations:
(1) There is a time limit to the Jutsus
(2) The edo Kages have their souls release in the same way some other edo were release by themselves - example of Gaara's father, or Sai brother.
In we don't have the two cases above, then, we can expect that SO6p is simply OP, but still I something remains fishy. He does not even address the case of the people who are in IT. He only cared about sealing his mother, congratulating team 7 and having fun with some chats.
in my opinion, priority should be placed on releasing those who are in IT, but rather, it was as if the kages do not know that people are in IT anymore and they are leaving with settling the issue.
This being said, unless IT has been already release, we may have been tricked by Kishi again. It may appear that Hamura was actually a villain, and he disguise himself as hagoromo to trick the Bijus and everyone else.
Besides, I found Kurama's reaction to Naruto unpleasant and I still wonder why he did that, especially that Naruto helped them.
Well, I may be overthinking it, but it could turned that everyone is already in that old geezers Genjutsus. After all, he came out from Madara's body.