Due to the nature and speed in which the NHL is evolving this contract is about a lot more than just William Nylander and the Toronto Maple Leafs. The last several years the league has seen an incredible influx of young talent that have proven to be impact players much sooner than previous decades. This season might see more players in the first 5 years of their pro career in the top 60 of scoring than ever before. Traditionally players coming off an ELC are usually signed to reasonable mid term mid cost deals, usually a contract that doesn't end in them being a UFA.
That third or fourth contract is most often seen as the payday, as these players have payed their dues and established themselves after many years of productive play. There are some notable exceptions(McDavid, Draisaitl, Eichel) that can be said to have changed the market, but for the most part players of this caliber aren't usually getting 8 years. Some recent examples of players on good money deals during their RFA status and what are likely their prime production years are; Mark Scheifle, Nathan MacKinnon, Alexander Barkov, Brad Marchand, Filip Forsberg, and even John Tavares. Some players sign smaller bridge contracts during these years like Logan Couture, Joe Pavelski, Nikita Kucherov, and Max Pacioretty. The contracts these players signed coming off their ELCs can be said to be typical of the tradition in the NHL of placing an emphasis on "earning" a big money deal through consistent production during the RFA status.
What Nylander and his camp are recognizing is that having this kind of talented youth producing like a premier player in the NHL has become more valuable than ever before. The NHL has trended towards youth, speed, and skill over veterans who might provide more "presence". With more young players proving their worth in shorter time periods and this contract being situated in the highest of profile markets in Toronto, it will have an important impact on setting the market for the next batch of 60+ point RFAs, of which there are certain to be more and more of around the league.
Getting your young talent on good term and good money is of utmost importance to an NHL franchise in a hard cap system, even with that cap increasing. Nylander and his agent are absolutely right to be holding Dubas's feet over the fire and I'm sure the rest of the league is very interested in the outcome.
This is a very important contract in modelling what some of the League's other young talent are going to be looking for over the next 5+ years. Will they be willing to take less just because they are "young" and are still Restricted Free Agents? Or will they demand to be valued for what they are as possibly the most vital pieces of an NHL team's future?