The presence of mini-games has already been proposed in the "Wishlist" topic (where belong most suggestions).
"No mini-games. Lockpicking will be item based and dexterity based." -Taken from Update #9.
Whether it refers to lockpicking specifically or any other mini-games, I don't know.
As for surprise attacks (more generally randoms encounters), should you play solo or in co-op, I doubt it wouldn't work, given the nature of the game. It'd add to the fun in multiplayer for sure, but I guess it has already been discussed, it's quite a popular feature in RPGs.
Hopefully we'll have a words or two about it in a later update.
