User blog comment:Tommy,Klaus&Kol2012+/A theory about the empty guardian/@comment-3045936-20181213215633/@comment-74.132.82.188-20181213235615

The EP indicated that there would be some resolutions to relationshps in Ep 300. Maybe John is not back in the way Mary is back, but in some kind of dream, memory, or flashback.

With all of JDM saying he wanted to return if the script were right, I am not surprised or shocked. I bet there are others based on what we know of this episodes premise.