The future cup-contending core is:
Galchenyuk
Gallagher
Eller
Pacioretty
-------
Subban
Emelin
Tinordi
Beaulieu
Diaz
------
Price
That's not really how it works though. Teams that have won the cups in recent years had great young talent drafted early in the draft. We do have Price and Galchenyuk (and Subban) that we can count on, but I doubt Bergevin has any of those other names you wrote above as UNTOUCHABLES.
Team status change every off-season. Lots of things come into play. Great seasons, down seasons, injuries, playoff successes. A guy like Eller or Gallagher probably wouldnt have been so up high on our depth chart last off-season. Things change. Teams winning the cup don't identify a 'core', they just try and build the best teams possible, every year, and that's an everyday work.
You can never know when your team clicks and goes on a deep run. Look at us when we went to the east finals with Halak, that wasn't supposed to happen. But it did. We were not supposed to contend. GMs evaluate their teams as the season goes along and make necessary changes, depending on if they are contending, middle of the pack or rebuilding. Nobody knows where they will be at the start of the season, regardless of their core players.
What I'm saying is basically, Eller could never be the same after his concussion, Tinordi could become Komisarek and Beaulieu could be traded in a package. You just never know. Therefore I don't think we should identify a window in which we are supposed to win, but just go along and make the needed changes when Bergevin judges necesary. For exemple, last year we were on top of the conference, but didn't make any major moves at the deadline. Even though we were 2nd, the 7th seeded Ottawa manhandled us. We missed our chance. We ran into injuries and cold streaks. Price had lost his confidence
I believe that ya gotta do what ya gotta do when the time comes. Bergevin will know when the team is ready and go for it. He hasn't established a time in advance though, and the youngsters we have right now might not be the ones with whom we win it all. Who knows if at the deadline everyone is on fire, and suddenly Philly offers Giroux for Galchenyuk and Bergevin is like, let's go all in. You can't know these things in advance.