Title? I don't need no stinkin' title.
Well, I disagree with the basic premise that at one point D&D was somehow "pure" or that it had a DIY, hobbyist roots from a company POV. I mean, maybe back in the mid seventies with the first initial releases? But it became a business long ago in the mists of D&D history.But back to the original subject, I don't know that D&D can ever sell out. It's a unique form of art that exists in its fans as much as its creators. Just as D&D in the beginning was monetized from the very beginning, D&D still has a hobbyist core today. It's always going to be a little weird. No matter how many great big epic campaigns Wizards releases, there's always going to be someone that decides that they want to run a world where everyone is a mushroom, or stat up a two-butted dragon to fight their PCs. It's a game that invites creativity in this beautiful perpetual motion machine.
But the real "hobbyist" side of things has always been the DM and table, that's not going to change even if the basic premise is correct.