Locked out of the Duty Finder.

[polyphonica]

Your pattern would lead to an exploit where a DPS would pair with a tank or healer just to get their near-instant queue, even though the tank/healer had no intention of running the dungeon and could just withdraw, leaving the DPS in an open (but only partially filled) instance. The open instance would give that DPS priority for getting the next tank/healer to come in, while meanwhile making the other players he/she was paired with have to wait it out with him in the instance rather than continuing what they'd been doing until a group was ready.

The tank/healer would take the penalty for that withdrawal, though. So sure, they probably could do that, but they can't just keep on doing it indefinitely without being penalized. And I'd still tend to think that, most of the time, they'd be better off just running the instance, since they often get role bonuses too (tanks in particular). The tanks/healers in question could do more or less the same thing you just described as it stands by simply exiting the instance after it pops, which then requires another tank/healer to queue with "in progress". At least this way you could open it up to anyone, regardless of the in-progress setting. That said, I agree that it's not a perfect solution either.

It's better for the DF to continue until it puts together a complete ready group, just like it does now, but have the player who withdrew be the only one withdrawn, rather than forcing the "withdraw" on whoever else he was grouped with as well. That means if someone Withdraws while his teammates Commence, the one withdrawing would be knocked out of the party, and the ones entering would be partied with whoever else the DF finds as a replacement.

I don't mind this in concept, but if it keeps the party at the front of the queue even after that one person cancels, it still opens the door to the same issue as above. The only alleviated issue, and probably your point, is that at least this happens when they're in the queue and not actually in the instance. However, if it does keep their "place in line" when doing this, then so long as one person withdraws when it pops, anyone else can withdraw immediately thereafter before it pops again penalty-free, unless they don't get any further choice. Right now, the penalty only applies if you withdraw when the queue pops, but not if you withdraw while waiting, so if a party member withdrawal takes you right back to waiting state, it's another way around it for the second+ person. A workaround there could be that you enter some sort of "Commence Imminent" state where withdrawing is no longer possible, or is treated the same way as a withdrawal when popped (i.e. penalty applies). This is sort of why I preferred the people actually travel to the instance, but it has its own drawback as you mentioned.

If you do any of this, the key would be to give some good options to the party leader to make decisions about what to do in various scenarios, as you could have a case where the whole party doesn't want to play if a given person is kicked out, which would just result in a different kind of failure (the party arrives to the instance, but instantly quits because their buddy got kicked upon entry; the party would have preferred to requeue with their friend than to keep their place in line). So if you have options like this, then perhaps it makes sense why the party leader could end up with some penalties themselves as well.

Anyway, trying to this in a way that's fair and also doesn't open the door to loopholes or workarounds is tricky. But it does seem doable, and in the end, having tools for a party leader to better manage and take responsibility for their party when enqueued could be its own benefit too.