Wow! That's a really neat theory I never would have though of and I'm sad it isn't true. I do think it works out better as Ring a ding fits the camp and spectacle heavy expectations Russell has put forward.

I love the Dream Lord as well! However, I hate to say it, but Doctor Who already has a far better contender for a God of Dreams. Zellin from "Can You Hear Me?" is a God like being who could definitely fit the bill. Also, if the Dream Lord returned, I think they would have to be recast, as Toby Jones is getting older, and you want that character to reflect the current doctor a bit more.