I'm not sure if a net "trap" would work all that well. Even on very tight maps, like Labyrinth or Canyon Ambush, there's still quite a big of room to fly around in.
It's true there's often enough room to manoeuvre around obstacles, but even then, why does the mine launcher exist if it's always possible to avoid obstacles?
It would be quite large, at least the width & height of the average balloon, if not bigger.. but even then, it would definitely be avoidable so long as the pursuing pilot has their wits about them.
It's not necessarily something you'd deploy and just leave hoping someone hits it - it's more akin to the Tar Barrel, where you only use it in close proximity to other ships.. except it's more focused in the area it covers, and possibly just takes the engines down instantly if hit, rather than damaging the ship in general.
I do think a net gun work be interesting- like, if you hit the engines it slows the other ship down for a time?
This is the bit I haven't quite worked out yet - depends on how it fits into the general balance of the game really.. on the one hand, it would be most effective if it were capable of breaking engines outright, but on the other hand if it proves too easy to use, it might be better if it were simply to slow enemies down (or even screw up their turning ability) for a period of time.
I don't know if it's possible to apply different effects from a weapon depending on where it hits, but if it is then maybe both could be true, with only a direct hit on the engines causing them to break.
That way it could be used by pursuers to snare their targets, while escaping ships could make use of it to put some distance between them and their pursuer.
I'm also wondering if various ammo types might have some effect on how it behaves.. for example, incendiary ammo could create a flaming net that causes persistent fire damage for a few seconds in addition to the slowing effect, or heavy ammo could create a much heavier net that causes a much stronger slowing effect, but has a tendency to sink to the ground after a very short time in the air if it isn't hit.
Can't really think what the other might do..