I'd say they'll probably make skeletron a boss within the dungeon rather then fighting him outside. Much like Golem. Or maybe they'll be adding more to the cultists since the cultists are the "dungeon coven" as stated in the achievement after beating them. Maybe even solar cultists? Who knows!
One thing's for certain, whatever it is, it'll make people wanna come back to the dungeon and that's what I like about it. Since I do feel like the dungeon needs more love then what it is already (not that it's bad, just needs a little more "omph!" to it).