Spirit, AKA WDW1974, is/was an insider here. He doesn't really post anymore, but he had a very good track record and broke a lot of news about both Disney and Universal (like Tower of Terror at DCA being rethemed to GOTG and Diagon Alley having a train transport between parks). From what I recall, there were plenty of other people who reported on the HM restaurant rumor however. I don't remember what Spirit said about it specifically.
I believe the idea has been kicking around for literal decades now. There was even once a conceptual proposal in the 90s to retheme the Harbor House to tie into the ride. Basically a haunted harbor/ship theme (based around Captain Culpepper's backstory). Though later concepts apparently involved some kind of new building behind the ride based off a haunted ballroom. Probably more similar to the ride's ballroom scene.