For him to get to that 9-10 million range he would need a 90+ point season and/or to lead this team deep in the playoffs, and even them, considering that he would be a RFA it may not take that much.
Right now, i think we have a pretty good reference in Tarasenko's contract, therefore, giving him that same contract is a mistake, much less pay him 8M.
Anything between 6 and 6.5 is a good deal for both sides, 7 would be too good for MacKinnon.
I could see MacKinnon not wanting a long term deal at 6M right now, and wanting to bet on himself having a great season and taking a better deal next year, and if i'm Joe Sakic i'm OK with it. Let him try. Let him earn the 7 - 7.5M deal.
For him to get to that 8M range he would need an 80+ point season along with 35+ goals, imo. And while he has the potential to get there, i think the odds are that he doesn't.