Not any mod specifically, but I'd like to see more adventure in mods and modpacks. I think the hole concept of mods right now is sitting in a base crafting my heart out, but I want to be REQUIRED to go out and adventure. I love Twilight Forest's concept right now, but it doesn't effect ANYTHING else. I want to be forced to kill a boss or find a special shrine to be able to make things. Maybe this already exists IDK, but I would love a modpack that does this. An example of what I mean would be something like, I have to kill some mob in the nether that drops a crystal that is REQUIRED to make a lava generator/dynamo. So basically the only way to use lava for power would be to kill that mob. I want this because I never have decent goals, and I always end up getting to a point where I feel like everything is done. I want to work for it more without it just being more crafting.
I agree here, there's not enough exploration-oriented stuff in a lot of the modpacks. I would like to see more mods that add rare terrain features, or things to explore or discover. There was one in Mage Quest (Ruins I believe) that is a good start toward what I'm thinking of.
Edit: Actually, you know... it wouldn't be terribly difficult to make such a mod myself. No new mechanics or mobs or anything, just some worldgen. The trouble is (as always) not getting bored with the project an hour or so in...
That said, combat is an extremely difficult thing to balance when mods are involved, because plenty of them nowadays offer armor and weapons (which can be obtained by largely holing up in a safe area until you climb the tech tree the whole way) that render vanilla mobs trivial. So it'd be difficult to design bosses that present a fair challenge to players without downright requiring that they spend X amount of time holed up in their base.
Also, have you tried Departed? It's very heavily adventure oriented. The only thing I don't like about it is the mob spawning in broad daylight.