Nah, this is not the first time that his email was hacked, way back in 2014,
satoshin@gmx.com is compromised.And we all know that he has left already, so it's better to really stop with this kind of speculation that he is back, because he won't.
I know why we can't know but his password would be a good clue to getting a more solid picture of who he was.
He did come to bitcointalk after creating the bitcintalk forum and creating bitcoin's software, I'd imagine if he came back to develop things (or stuck around under a pseudonym) he'd bring things that were built well and not come back with an idea of something he might make.