While in principle I can appreciate the idea of it as I've been in that same situation trying to join a friend or FC member in progress I'm not really sure how they would be implemented it's not really as simple as you think looking at how the DF works. Unless they introduced search terms somehow and then it'd just make things way more complicated and give the servers way more to do for something that while annoying isn't a game breaking issue. I'm not exactly sure what search rules are used for joining a party in progress if ones that have been going for longer get priority or it's just 100% random.