To be fair, he's asking advice about managing his relationship with his wife and being a new parent, not advice on cosleeping. My daughter's mother willfully ignored all the advice about cosleeping and chose to continue despite my best efforts to convince her otherwise. For every child that dies of SIDS as a result of cosleeping, you'll find 10 that were "just fine". You're not going to change human behaviour, if a mother believes that that's the best way of doing it then you won't change their mind.
Putting the risks aside, I've said it a couple of times already, he is facilitating distance between himself and his partner. So the bed sharing in the spare room will be having an impact on the relationship, and isn't a good thing.