I personally feel that this is the thing in which the game is most lacking... Mob difficulty does a lot in regard to how fun the game is.
If I do the work to improve the mob difficulty, and post an updated version of the mobs mod, will you add it to the game? I can also split it into the df_caverns mob pack while im at it...
I can also add mob spawner blocks while I am at it, although I will not make recipes or otherwise make them obtainable in game... that can be left for when and how you decide that you want that. Also, the spawnners can use node timers.
If you want me to do this, post a list of general guidelines I should keep in mind while making the changes, so that it matches what you have in mind for the game.