That why the Flyers will have to continually draft defensemen. I think than can realistically keep four if one of them is Morin since I don't think Morin will ever be expensive. That means if all of Provorov, Sanheim, Myers, and Ghost turn out, one will likely have to be traded. But you are talking when these guys are near 27 years old so many years from now. Nothing to worry about. I actually expect one of them to be moved when the Flyers are looking for that final piece to the puzzle.
I think they will be fielding calls from teams looking for a good young defenseman and if they can get good value for a center they like I think they will and should pull the trigger. There is no rush but it will happen at some point. Its just good asset management. If I was a western conference GM I would be trying to trade for one of them now before they get too established. I think it is already too late for someone to reasonably trade for Provorov.