I think this was from at least a year or so ago; it was certainly not 5.16 based. It may have been recced at some point on Crack Impala or one of the other reccing communities.  I may be remembering some details wrong; the denouement is under the cut.  

Dean was in heaven.  He was bored. There was a wall along the border of heaven. Dean climbed up it on the heaven side, and Sam from the other side.  The other side wasn't hell, but it wasn't a lovely place, either, and Sam was kind of feral; I think Dean didn't fully remember or recognize him.  It ended up Sam/Dean; if they had sex, Dean was going to be kicked of heaven, and that sounded like a good thing to him. 

Does that ring any bells for anyone?

Thanks in advance.

ETA:  found in comment!  Only the Good Die Young, by smallcaps .