The more options they add, with stuff like non-standard parties, the worse selection and queue-times get. If they were to add an option to tell DF you want non-standard parties then those people choosing that option would essentially be picked out of the pool of players to be put in a separate queue with only non-standard party applicants. Both of these pools would have worse queue times because there would be fewer applicants in each pool than there would be if there would only be one joint pool. The more options like this you add, like only being put up with people who have previously cleared an instance, the more you segregate the queues and the worse queue-times gets for everybody. There is already an option for non-standard parties and that's via PF, your FC, a LS or /shout.