But the subject of the wiki page is the observed effects on wives (specifically in Japanese culture), not husbands. There's surely plenty of literature out there on how retired people feel.
It might be worth linking the two together at the bottom of the Retired Husband Syndrome article.
How does that feel for them?
I'm 1000% positive that there's heaps of research on this, just google "study on male retirees"
Imagine if there's an article about what the psychological effects are if you have a family member in deep coma for many years. You're complaining that that article isn't talking about the effects of being in deep coma for many years on a person. They're different subjects!
I don't believe "RHS" exists as a real medical condition. It sounds just like girlies being girly, with teddy-bears and social circles and so on; and blokes being blokey and controlling the remote. This is just people being people.