p.s. Remember that if you open source it, anyone can use it for anything they want, subject to your license terms, even if the things aren’t things you support. Think about it carefully.
That activity would have your name attached to it too. Damn tough to avoid no matter what you or they say. That will be due to your non action over the years.
That was not wrong, or bad. It is just what you did. And from what you write, it worked out nice from your point of view. Nothing wrong with any of that either.
Lots of people jammed on your beats and maybe the world is a little more fun or something, right?
But, you will have sold the right to them and all that, and that ton of views could mean a ton of negative feelings headed your way too.
As others have said, get real legal advice. Now. Please.
Them wanting exclusivity and you have to believe they know those beats are all over the place, totally begs the question, "why?"
Say they follow through on the threat?
They remake it, somehow and then what?
Seems to me, using your beats or theirs all leads to the same place and that is whatever they want to associate with something they own has to exist out there with all the other efforts and that I bet just won't work for them.
Someone, somewhere is going to just start cracking down and the real question seems to be, "what will you do?"
If you opened it, doing something fairly solid that allows what is happening today to continue, that's a potential pain in the ass. Worth paying you type pain in the ass.
If you do nothing, they will include you in whatever it is.
If you sell to them, you get paid, and they crackdown and could mention you a lot to deflect from them.
Maybe you make something new, and tons of people know you created the existing stuff?
If, if, if...
Get some real advice and figure out what is worth what.
Will they give you enough money to not give a fuck, for example? You said it might be a lot. Too much? My gut says probably.
Or, maybe you just learned your beats have more value than you realize.
Maybe in tandem with opening it up, you tell the tale and get some money and or somehow make it far less worth it for others to try and take up the space your beats now occupy? Maybe make it clear all uses are OK, but can you get some help with legal...
My major question is, "Do what the right way?"
If it were me, I would try hard to find out before doing anything, and find out how urgent it all is and what the impact is to all those people out there using your beats, and how you really feel about all that.
And however you feel is what you feel. What you value is the same way.
Good luck.
Get that advice.