Yeah, there's no doubt in my mind that this is a bad thing for the game and VR in general. We need less platform lock in, not more.
They will likely be forced to 'mess with mods'. Unfortunately the mods enable song piracy, and Facebook is a much more lucrative target for litigation.
Being able to play user-made levels is the single reason why I love the game. I’d be willing to pay for an Apple Music-like subscription to have my favorite songs as levels but the community ones are way more fun than the official stuff anyway. I wouldn’t support it if it ended up turning into Guitar Hero DLC-hell.