In regards to the idea that D&D (and RPGs, in general) need to go more mainstream to succeed, I don't know if that is 1) possible given the nature of these games and 2) really the kind of thing that would help the actual game.
1) The only real way I can see to make these kinds of games more mainstream (i.e less inherently uncool seaming) would be to remove the tabletop for something more larpish (a field perhaps), then take the 4-6 (or whatever) ammount of group players and break them up into two groups, maybe increasing the numbers in both groups (maybe 6 per side for example), then taking the swords and spells etc. and replacing them with some kind of ball, and finally reducing the GMs responsibilities to something more referee-like.
2) Mainstream crossover doesn't really help the thing crossing over, does it? (I'm not postulating a fact, but asking a question.) For instance, did the Spiderman movie apreciably help comic book sales, or just movie attendance? Sure it would be neat to here 'normal' people discussing common rpg tropes in the FoodCourt, but if none of those people are actually playing the game, did the hobby survive, or did the tropes just jump ship?
For the hobby to survive and the "Next Big Thing" to succeed, it doesn't need to garner a new audience, it needs to stimulate the the immagination of the existing audience (and perhaps pull back old players) in a sweeping way. The game doesn't draw new people, the gamers draw new people.
DJC