Why are you saying it again?
If you're looking into their runs on raider.io to figure out if they might be boosted, you either take it way too seriously or are not in the bracket these changes are aimed for. I'd like to meet the boosters who can time a +22 key with 4 people. Those are some hardcore people.
The "number" would be dictated by other players. There are a lot of times when leaving a key is the best thing to do. I'm not out to blanket punish everyone who leave first. You're saying that, not me. I'm for a small incentive to look out for others. It doesn't need to be a number everyone can see. A gold star next to your name, if you meet the criteria, might be an idea. Up/downvoting other people (that only you can see) and then showing those people in the groups afterwards would be anothers. As a precursor to friend/ignore list. As the ultimate solution to this problem is to have your own network of people you like to play with. Pushing this with easy UI change, that require no effort from the player isn't the worst idea in my opinion.