The way I see it is this: Halo 4 had good singleplayer but shit multiplayer and got an 87 meta. Halo 5 had good multiplayer mechanics (though a poorly implemented MP lootbox system) but shit singleplayer and got an 84 meta. That tells me two things: 1. Good singleplayer is somewhat more important to critics than good multiplayer, and 2. If 343 can pull off both good singleplayer and good multiplayer in a single game they can bring Halo meta above 90 again.
Now I'm definitely hopeful that singleplayer will be better than Halo 5. The main reason that Halo 5's campaign was bad was the writing, and they dropped the Halo 5 writer, Brian Reed, soon after it released, and hired a Bioshock writer and a Batman Arkham writer to replace him as co Narrative Leads. That's already a positive sign. Add to that the fact that Joseph Staten, one of the Halo 1-3 writing leads, got brought in to oversee the campaign development last year. They also made several other smart choices for the campaign, a return to the classic art style, setting it on a Halo ring again, a return a more classic sounding soundtrack. I'm definitely hopeful that singleplayer will be much better than Halo 5 and probably Halo 4 as well.
Multiplayer wise, they basically just need to copy Halo 5 mechanics, but remove the lootboxes, which we already heard they did (microtransactions are now non-randomized and cosmetic only, with in-game earning options for all of them). The rumors of a new Big Team Battle mode replacing Warzone also sound very promising to me. Another area where 5's MP suffered was not having enough maps on release, I'm hopeful that since they will have 6 years total to work on Halo Infinite (compared to 3 years for Halo 5), they will have had plenty of time to design a large number of maps for both arena (small scale) and this new Big Team Battle mode, plenty of weapons and vehicles and cosmetics as well hopefully.
So yeah, I'm definitely hopeful that Halo Infinite can top Halo 4's 87 meta, which is why I predicted 89 for now. But I do think that 90+ is a possibility if they play their cards right. Hopefully the singleplayer graphics are a substantial leap when we see them again, that would certainly help lock in that 90+.
it's definitely in the realm of possibilities. They had the time, so they better deliver. I have hope that Halo and Gears will rejoin Forza in the 90+ club once again. (and Fable to get it's first 90)