I think many of us would welcome such a wiki, but with 8,000+ Marriott Bonvoy properties across 139 countries and territories, collecting accurate data and maintaining a wiki would take a huge effort. It's not something I would volunteer to do.

The right place for laundry room details is Marriott.com. Most (but not all) individual hotel websites on Marriott.com have an Amenities section that's supposed to show what facilities that hotel has.

Marriott claims that the Amenities section for each hotel tells guests whether or not the hotel has a self-service laundry. See https://help.marriott.com/s/article/Article-23501

Unfortunately, the information is unreliable to the point of being completely worthless. I have upcoming reservations at five hotels in Italy. All of them either indicate they have a laundry (complete with the washer icon) or they don't have an Amenities section. I've already figured out that none of them actually have self-service laundry facilities.