Instant action will be a bit repurposed - it will be a "take me to a different fight!" button. It will always work for a more balanced fight, and it will always take you somewhere you haven't been recently if possible. So if you don't like the fight you're in, hit IA and it'll take you somewhere else on a different mission. If it's always working as a population balance mechanism then we can safely reduce the cooldown on it so you can more easily hop around from fight to fight (or more accurately, mission-to-mission) if you want.
Edit: One caveat is that we plan on having different instant action rules for newer players (example: under BR 20) so they get better fights, even if it may imbalance the fight a little. The goal there is to improve things for new players and give them less riskier locations so they are less likely to get a really brutal first impression of PS2.
We plan to have specified drop zones for each outpost, both for attackers and defenders. This guarantees that drop pods come down in appropriate locations for each facility, and attackers and defenders don't come down in the same locations. We wanted to do this as part of drop pod tuning but it got postponed for performance optimizations. Can't give an ETA on when that will happen, but it would be nice to get it in as part of the mission feature.
Edit: and no the drop zones won't be known to players; there will be multiple areas for each outpost, those areas will be big, and the drop pods will be randomly spawning in them, so camping drop pods won't be any more possible than it is today.