The book will most likely use their design goals of "Action-Oriented Monsters"... a concept that he came up with that basically introduced 4E-styled monster abilities to all creatures (and which you can see suggestions of in both their Strongholds & Followers and Kingdoms & Warfare books.)
Long story short... all monsters will have several Actions to choose from, and at least one (if not more) Bonus action and Reaction. So there is always something the monster can be doing beyond just like a pair of "claw swipes" or whatever. In addition, his Action-Oriented design includes a variation of the Legendary action idea... wherein a creature has like an additional and different bigtime action for each round of combat. First round the creature does X, second round the creature does Y, third round it does Z, and so on to give us a "story" of what that creature does over the course of a fight. Now I don't know if THAT mechanic is going to be given to every monster in the book (or if it's meant for just the Boss-type monsters), but I do expect it to show up somewhere within it.