As much as I like the Turn-based of DOS2, I believe that more instances like "attack of opportunity" could add a lot of variety and unpredictability to the battlefied.
A couple things that come to mind:
Cover- very obvious, especially considering that Elevation already exists, to a degree
Reactive turns: instead of standard progressions, powerful enemies and/or players with a special trait could opt for this: take an action EVERY time someone finishes a turn. It may sound OP, and in fact it would work mostly for bosses, but I am a fan for rules as symmetrical as possible
Attacks of opportunity: possibility for them to appear with ranged weapons and/or spells too
Triggers (?): the possibility of setting counter-attacks or immediate, automatised reactive actions (like, get injured: drink a potion IF you have it in inventory etc).
I understand that someone will immediately argue it could be a lot of work: this is a pre-alpha, it's supposed to involve potentially very different and brave possibilities.
