What you've got is how every MMO on the market that has Qs for PVE and PVP do it. I know it seems to make your arguement more valid (even tho it really doesn't) to make it seem like they were simply to lazy to come up with the Q but not really in the Q idea of stacking. Under this solution you'd still take forever to get a FP Q to pop cause PVP pops are dime a dozen and you'd have a cloud of perpetually stuck people in the limbo in-between the two. Dan is #19 and gets out of his PVP Q and gets another 30 seconds later, so he has a whole 30 seconds for the PVE Q to pop before he's back in limbo again.
How is this in anyway a workable solution? How much of the games resources are going to be tied up keeping track of the massive cloud of people in the Q but not really because the are in a PVP match at the same time? Yes eventually they would get lucky and get a pop inbetween the two but in the meantime the only reliable way to get in a PVE grp is too...not Q up for another WZ...just like they are asking you to do now.
Obviously you missed where I wrote about a notification to the player, telling them that they are at the top of the queue.
If they choose to continue pvping instead of waiting for the flashpoint queue at that point in time, that's their problem.