A dungeon master type system would probably work best. The DM would have an overhead map view to place units and tell them where to go or what to do like an RTS game. The ambient mobs would still do their own thing though. There would also be a free cam mode to spectate the battle better.
Maybe the DM could have a modifier system where you can pick a certain number of mods for your various troops types, like more health, more damage, faster reaction speed, faster spawn cooldowns etc. Kind of like deed modifiers, but less powerful and more customizable.
As an example, you could upgrade your SV to take alot less damage from grenades, making grenades less powerful verse SV patrols.
There’s 2 limiting factor to this system. Firstly, what would the incentive be for the DM player to play in the first place, maybe some DM mode exclusive rewards, like character skins, frames etc? The second factor is, would it be worth the development time? I’d argue it wouldn’t be worth it right now, but maybe if this year gets alot of new content then a DM type mode might be worth it for next year.
As for a PvP system like KF2s, L4D etc. i don’t think it’d work very well or at all. VT2 just isn’t designed for that type of gameplay.