First, remember that it would work alongside the kick option
The exponential lockout could be another option too, as long as it wouldn't reset for X hours and they could still bypass it by going with a premade group. As I said this isn't just suggested as a punishment, but as a correctional.
As for innocent people leaving, it's ok if people leave after trying and trying and seeing that they can't beat it, but those are a minority in the DF and you know it. Some just try until there isn't enough time left, and a majority just leave after a single fail or two (or simply if they see something that they don't like). Also, I think that, as of now, the system doesn't punish you with the 15 minutes delay if that's the case (at least I haven't got it when I've kept trying to help someone), so I don't see what would be different in this situation. They just need to check how often someone left a duty and make the system act against those that do it compulsively. They could even check the amount of times the bosses were restarted (wipes) to make it even more fair to those that at least try. As I said, dev data should be considered and analyzed if something like this would be implemented, but they need to do something and I think that MVP won't be enough.
That will be solved after they implement the gear checks to the DF (with requirements introduced by the devs, not one of those unrealistic players that we have in the game).
Regardless, the vast majority of quits that I've seen in primals haven't been because people were bad geared or we couldn't kill the boss, but because someone failed once or because God knows why, because they just leave and don't tell why, thus not helping those that they might think that should improve. I understand that some people get frustrated if they've been dying in their other tries, but that's not the fault of the people in your current party and you shouldn't be impolite towards them just because they are humans and make mistakes (even if some people treat them as if they were bots that are there just for them to use and discard). If you're frustrated, please, go ahead and take a break. Both your mind and your fellow players will be grateful, and you'll be able to tackle the fight with a renewed spirit and a fresh mind after that. Doing otherwise you're just punishing yourself and those that are not at fault. Oh, and that would also help you to avoid the suggested penalty, if introduced.
They can't do much about it, at least regarding dps queues. I think that they're already going to give bonuses to people tanking so that more people are willing to try it, but... Anyway, if you say that because of the reserving instance issue, I've not had it for two weeks, and they're going to put more servers for it this month.