I think this is a factor that some aren't putting enough stock in, especially if you want Crosby and Malkin to produce as much as possible. As a team, they don't really have the prospects to be able to plug into major NHL roles with the amount of guys they're going to be selling off. Getting these guys like Tomasino and Hoglander for cheap with intent on increasing their value can fill some of the gaps that the prospect pool has.
It would be one thing if acquiring Hoglander would block out a top prospect from taking that role, but who would Hoglander be blocking from playing on Crosby's LW? There just isn't much talent there. Adding more guys like Hoglander and Tomasino (especially on D, I think they need both a LD and RD) for the cost of 3rd or 4th rounders is what they should be doing to fill out the roster. Even if you go super prospect heavy in the NHL, you don't really have enough good prospects to fill every role.
Assuming they won't be able to move Hayes or Acciari in the next year, I'd be advocating for a forward group like this for next year:
Hoglander-Crosby-Rust/Rakell (trade one of Rakell or Rust for futures)
McGroarty-Malkin-Tomasino
Bunting-Lizotte-Beauvillier type of UFA or trade
Poulin-Ponomarev-Hayes
Eventually plan on trading Bunting, Hayes and that Beauvillier type of UFA to promote guys like Broz, Koivunen and whatever other WBS player deserves a promotion.