I think the negative stigma of being a "D&D player" by the general public who is even familiar with the name of the game is probably THE thing that will keep D&D from ever becoming as successful and mainstream as we would like it to be.
The original "boom" in the late 70s, early 80s was new- fresh. And the many people not involved had no way to form an opinion of the game yet- and the stereotypical players of said game.
30 years later it's quite different. Oh sure you have a few moderately successful actors who play, some who mention they used to play, etc. But the general public does not have nearly the bias towards other entertainment like board games, and computer/video games because those products have been ingrained in our culture for people of all stripes and types as "normal"- whereas D&D is still seen as "dorky, geeky" etc. Sure properties like HP, LOTR and SW have sold to the extremes to the masses, but going to the movies (IOW- mostly are "books" for people who don't feel like reading- present company not included) and RPGs are very different things,
Then on top of that you have all the issues of modern complex systems with big barriers to entry, time & scheduling necessary to play, and getting everyone together to do so on a consistent basis.
So, IMO, Ain't gonna happen- until there is a wholesale turnaround in the perception of the D&D name, and stereotypical gamer image it conjures, by the masses of non-gaming public.