If you haven't noticed, plenty of teams have young cores. You can build a great young core, but everyone seems to have one these days. Teams with young maturing cores include Ottawa, Carolina, San Jose, Buffalo. Florida, Edmonton, Calgary Anaheim, Atlanta, Tampa Bay, Montreal, Minnesota and Nashville all have good young cores. Washington, Pittsburgh boast some scary talent. Columbus has a nice collection of prospects with top end potential. Chicago and St. Louis are at the bottom of the food chain now, but will be in a position to gather up lots of young talent. That's basically half the league, if we consider teams that are young and talented.
This ignores all the teams that are still strong contenders like Philadelphia, Detroit, New Jersey and Dallas who are still strong teams or middle of the road teams like Colorado, Vancouver and the Rangers who can come up and surprise every year.
You can build a great young team, but a dynasty is almost impossible with the kind of parity we're looking at. With the number of good young teams out there, even the best preparations can go to waste if you run into injuries or a cinderella team. The window of opportunity is extremely narrow. Case in point was Ottawa this year. Who knows what will happen to that core?