He has a full NMC, so it may be a bit of a moot point, but there should be a "None of the above - explore the trade market" option.
I know it's complete taboo to suggest trading him, but in a league where MacKinnon just signed for 8 X 12.6M, Tkachuk just signed for 8 X 9.5M, Pastrnak just signed for 8 X 11.25M, Fox/Makar recently signed for under 10M (granted as RFAs, but based on Matthews last contract, we obviously didn't bother distinguishing between RFA vs UFA contracts at that point), etc, I just don't know if I could accept any of these options.
The cap is going up, sure, but options A & B overlap entirely with the MacKinnon, Pastrnak, and Tkachuk contracts (+ those contracts actually last a bit longer), so there are literally zero years in a higher cap world that would only be apply the Matthews. The 8 year contract overlaps with those contracts for 7/8 years, so there's no justification for such a massive jump in pay.
It boils down to a principle thing. I don't expect players to take discounts, but if you're going to play for the Leafs, where you can get paid in massive signing bonuses, where the support staff and organizational support of the players is second to none, where you can make a ton of extra $$ on the side in endorsements, where you get to live in one of the more interesting cities in the league, etc, then you should at minimum be willing to sign in line with what similar players around the league sign for (MacKinnon being the best comparable). If Matthews signed 8 X 12.7-13M, nobody would be saying he took a "discount", yet here we are with 15M+ being thrown around for his 8 year deal.
We overpaid last time, which cascaded to overpaying Marner as well, and it massively hamstrung is and we only made it past the first round once. If you want a culture of buy in from everybody to doing everything you can to win a championship, having your top stars squeeze every last penny to get paid well above market value, in a hard cap system where that directly takes $$ out of teammates pockets, isn't the way to build that culture.