Clair Obscur Expedition 33 kind of has the gaining abilities from mastering equipment thing you mentioned, it’s not really equipment in that you can’t see the items being put on, but you equip items that give abilities and after a few battles with it you master the ability and can change to another item but equip the ability through a separate resource pool.
YARG and Clone Hero (and others) exist, they’re obviously not as big as Fortnite but big enough. Also the Gibson thing you’re referring to is from CRKD, who started putting out new guitars over the summer, plus the already mentioned PDP Riffmaster. So it seems there’s at least enough demand out there that 2 companies started making new controllers for these games.
Even if the AI bubble bursts by then, chuds will probably come up with some new bullshit to keep the market inflated, just like scalpers, crypto miners, and NFT weirdos before them.