To further elaborate on my previous post, and what I somewhat expect will make it into the game :
at some point (possibly even the next update) some form of stat cap will be introduced, alongside the ability to upgrade the cap, most likely via sacrificing gobbos or selling women (or both? sacrifice certain number of a monster to increase it's stat limits, sell women for money that can then buy upgrades to the keep/defences?).
I can easily see things like traps being implemented too, as the amount of road leading to the keep is fairly long, and in traditional tower defense style, traps are a staple of those games.
honestly, one feature that has been shown but not implemented (yet) is bosses, which is possibly a neat way to get unique units (maybe a special animation/scene could play when the boss gets defeated before they are captured) which can be a nice call-back to MBM.
I also suspect that might be how we will gain new monsters, as the current game has waves of women and nuns, and also gobbos. Having Orcs/werewolves/whatever attack and be gained/captured could be an interesting mechanic... or that could be done via raiding...
ah, so many things that could be done... wonder what the dev will do.