Edited Jan. 4, 2019 at 8:44 a.m.
I'm worried that a defense corps of Provorov, Gostisbehere, Sanheim, Myers, Morin, and Haag will not ever be good enough to shut down the likes of McDavid or Matthews while also putting up points. They're all nice players with potential and tools, but the Flyers could very well end up having to trade for at least one more elite #2 defensemen. Myers or Sanheim will be probably gone in 2 seasons due to the expansion draft, so one of them will have to be traded for something. The Flyers could alternatively trade the worse player out of Sanheim or Myers in 2 seasons for a pick. Gostisbehere isn't going anywhere until someone else proves capable of putting up 40-50 points per season. While it is risky to trade a potential future star, it's also risky to forgo the trade value of a bluechip prospect that never lives up to its potential.
I'm not really a big fan of Rubstov, but he still has some value for the moment as a former 1st round pick who has some excuses (lack of opportunity in Russia, lack of time to build chemistry in juniors, and some injury trouble). Even if he turns out to be decent, the Flyers likely won't have room for him above the 3rd line.
I don't like trading Frost and wouldn't include him for the vast majority of the players in the league.
In 3 years, they would still have Patrick, Konecny, Stone, 2019 1st round pick, Lindblom (if he continues to develop), maybe Giroux, maybe Couturier, and whoever develops out of Farabee/O'Brien/Ratcliffe/Strome/Vorobyev/Allison/Laczysnki. On defense they'd still have Provorov, Gostisbehere, Doughty, and Haag or Morin. In goal, they'd probably have a talented young starter in Hart, or maybe Sandstrom/Errson/Ustimenko. Eventually the Flyers are going to need to start trading some of these prospects when they don't have any more developing to do and the Flyers don't have any room.
If they don't want to try to win now, I'd alternatively like to see them trade players like Voracek and maybe even Giroux for talented young players. I don't want the Flyers to waste the rest of their prime fielding mediocre teams and try to start being competitive when they start to decline. If the Flyers keep them around, they will have a very short window, slightly later than the above roster, while Giroux and Voracek are still good and the prospects are approaching the prime (but not getting paid yet). Their value for the years until that short window would have been wasted. After that window, there is no guarantee that Patrick/Konecny/Linblom will be any better than Giroux/Vorack/Simmonds. There is no guarantee that Gostisbehere/Sanheim/Myers will be much better than Streit/Coburn/Meszaros. Finally, the players who replace the older players will be more young players that are a few years away from their prime.