A cartoon.
Transformers was started as a cartoon and now look at it. There is precedent for a D&D cartoon already so it's not a stretch to entertain the notion that it could be done again.
If it's done WELL, as in it's a decent cartoon with a decent story, decent illustration, decent characters, etc. and it's aimed at the young adult market (which is a bit of a misnomer because although technically a 'teenage' bracket, younger kids want in on what's cool for the older kids and parents tend to enjoy it as much as their kids and geeks of all ages tend to embrace it as well), then it could be huge.
It would also need to be done cleverly. There would need to be tie-ins to the D&D P&P game within the actual story. But it would have to be done in a way that's not obviously just a gimmick to push product. It would have to be done in such a way that was very well thought out and considered from many angles rather than just some writers brain-storming story concepts.
This would lead to all sorts of extra products. Figures, graphic novels, novels, collectibles and even a movie (that didn't totally suck). All the while growing the D&D brand and P&P game.