It’s not the system itself seems difficult to me, but the conflict with design of the mechanics that are already present which would take effort to deal with. Currently, a random chance of post-battle revival facilitated through a companion is the only one method that seems like it would be suitable. This could change if they add mechanics facilitating the proper taking of prisoners.
One problem that won’t go away though, is how adding capture mechanics that have to be applied in battle can quickly get complicated, as you can’t just have characters get captured during the battle itself. A capture in battle would be the equivalent of adding a certain kill, as someone who is captured is effectively dead and can no longer contribute to battle. Furthermore, you can’t remove anyone from the field, since every participant is represented on the battlefield at all times, meaning that a potential prisoner would also have to remain on the front line. After all, they can’t teleport off the battlefield. To take your net example, it would mean that the person restrained by the net would have to remain in that position until the end of battle for them to count as a prisoner, because they are not dead and therefore still a part of the battle. In the meantime, they would have the opportunity to escape by getting loose or being released by someone else. In other words, the actual capturing would still have to take place post-battle. For that to also work, the net would have to be persistent, rather than temporary, of which we don’t know yet whether that is the case. A club wouldn´t actually be fitting for a role like that, since it only stuns for a turn (which is more like a concussion) and a longer stun would be way too powerful (and basically mean you turned them into a vegetable).
The idea of taking prisoners in the middle of a fight would be weird anyway, since it isn’t really possible to take people prisoner in the midst of an intense scrimmage. It’s usually a group as a whole that surrenders. This’ll get better reflected in the mechanics once enemies can retreat.
As for save scumming, people are free to do that if they want, but a game should never incentivise it when it isn’t necessary. That’s just poor design.