It looks like we may find out in a few months, however. In a recent MMORPG.com interview with Bill Roper, Cryptic's Chief Creative Officer cracked a small window into this upcoming announcement:
"I can't speak to the specifics of what we're doing, but it's true that we have another game in the works. We won't be making an announcement until late summer, and we're still a ways off from launch. I can say that this is a game and a franchise we're very excited about. I think people are going to pleased and a bit surprised with what we're doing in terms of the game, how we make it, and even how we sell and support it. The game is being developed around new design principles merged with Cryptic's community-first approach to ongoing development."
Seeing as how the company currently covers both the superhero and scifi genres, a fantasy game would complete the trifecta. However, Cryptic's "In Development" page features concept art that seems to cover a more modern horror/adventure vibe. In any case, it'll be interesting to see if the D&D rumors are true, or if there's a wild card up Cryptic's sleeve.