I'm a tank and I'll be honest I never tick "in progress". If I queue for a dungeon I want to do the whole dungeon not just the last boss or hardest boss. Parties that lost their tank probably lost it for a good reason, you were making his/her life so re-queuing and starting over was preferable.

Since doing Relic I've gathered a nice number of DDs and healers on my friends list which I can create pre-made groups to queue with where I know everyone will work together without flaming and rage quitting.

If SE want to incentivize me back into the duty finder queues or groups in progress take a leaf out of WoW's book and offer bonus tombstones or a treasure box with a bonus drop for it. Tanks are the least played and highest gear requirement, don't make them even less fun to play trying to solve a perceived problem.