If the 5th wasn't going to be Matthews, he'd have been released by now. Unless one of the lesser knowns truly emerges as a big talent, the fight is really only over who is going to be #6 and who is going to make the practice squad.
That would be a terrible strategy. If Miami wants to try to get something for Matthews they'll showcase him in the preseason and hope another team has an injury at WR and comes calling. The last thing you want to do is just release Matthews right now for nothing...unless his attitude is so detrimental to the WR room, in that case you let him go but we're not at that point yet. You certainly don't want him latching on to someone in the division so he can share knowledge of the team. Worst comes to worse you trade him to a team for a conditional 7th round pick just to make sure he stays out of the division.