Mistwell
Crusty Old Meatwad
I'll call into question a different aspect of the OP's position: that of the universal appeal of Marvel or DC.
Agreed. Particularly in this sense - Marvel's biggest successes were for some of their least recognizable characters. Iron Man was a second or even third tier character. Same with Captain America, and particularly Thor. Black Widow? And next Guardians of the Galaxy and Dr. Strange? Those last two are like 5th or 6th tier characters. Even serious comics nerds never cared much about Guardians of the Galaxy!
Basic vague brand recognition is all they needed to get people to try the movies out. That, and good stories, good casting, those carried the day. All of which Hasbro is capable of doing with a D&D movie, or TV show, or whatever. There's no worse public associations with D&D as there were with Thor or Iron Man or Captain America - all considered to be silly characters by the general public before the movies came out.
Same goes for other nerdy franchises. Lord of the Rings had a negative nerdy association with many people, before the movies. Twilight STILL has negative association with it despite massive success. Hunger Games had fewer people who knew of it before the movies than people who know of D&D, and I bet Game of Thrones did before the TV show as well. And as people have mentioned, Transformers is a good example of this concept as well.