I don't expect much more than a 95, honestly. Historically, I believe the best-rated Mario game on Metacritic is Mario Galaxy with 97%. Sunshine/64 had low 90's. I'll be content with anything above 90.
I can't imagine the expectations of games nowadays. We're half-way through this year, and ONLY Zelda BOTW (both versions), Shovel Knight, Persona 5 and Mario Kart 8 Deluxe have gotten above 90 on Metacritic. Nope, HZD didn't even get a 90.
So, can we really jump to the conclusion that this will get a 99? (that was probably a joke). I'm expecting a 94-97 if this lives up to the hype. This has to be decently better than Galaxy, in other words.