I'm actually amazed it hasn't happend yet.
eBay used to actually CARE and shut down Mame auctions and related pirated auctions (e.g. 39-in-1 jamma boards, williams 8-in-1 multigames). However, about 6 months ago, they stopped responding to reports of these types of auctions. (the same time you could no longer send links to Mame.net's policy and stuff to back up reporting an item)
Ever since then, eBay is rife with illegal product. Now, don't anyone get into the discusion of "everyone is in violation by owning". This is an issue solely about selling and PROFITING from the games. And it is clear there are TONS of people profiting GROSSLY from this, and to me, it is just sickening.
I have no problems with someone making money from their own "NEW" work (e.g. encoders, joysticks, etc..) but not to those that sell property they don't own. I write software for a living myself and get very sick when I see people PROFITING from pirate sales of the products I write, and receive constant offers to "buy" my software at cut rate prices in my spam folder.
I think it's possible the core MAME people may stop publically distributing something and may even go so far as "recalling" Mame (making it a closed source and no rights to distribute).
Now that of course won't stop what's out there, and there is more than enough out there now to keep people "in the money" forever more. However any new work would be stopped, and perhaps that would be a good thing to keep from tromping on the rights of current games that are still out there (yeah, the 3 year + not actively sold rule isn't quite right since there are still Ms.Pac's making money for various route owners)
Of course some developement may continue by others, or those that want to optimize (e.g. AdvanceMame, Mame32Plus, etc..) and those that want to fix bugs of old games, and not add new ones. That would be a good think to everyone.
If mame stops now, it doesn't hurt me, but unfortunately it doesn't hurt the scammers either.
Mame has actually caused me to get into original collecting and refurbishing. I still havn't built a Mame machine yet, and rarely play any games, but it did get me to go get a few of my fav games and play them LEGALLY! (Not that it happens to everyone, but Mame had a positive effect for that for me)