While Xbox Head Phil Spencer talks about 343 Industries' current efforts on the next Halo (and past Halo games) for the Xbox One X, the developers have come out to speak on Halo 6 themselves.
We knew Halo 6 wouldn't be making an appearance during Microsoft's E3 2017 presentation, but it appears to be that even though the game is allegedly coming along well, we won't be seeing it anytime soon. The Halo developers took to the Halo blog to reveal how soon we can expect to see Halo 6 (not soon).
"That being said, for some people – like most who are still reading this blog – the Xbox media briefing was bandied about as much for what it didn’t show, as what it did. Specifically, a new (or old-made-new) Halo title. For some folks, their despair stemmed from a lack of remastered fight-finishing. I know I know, we should have told you ahead of time to not expect anything like that. Others were hoping for a tease of things farther off to come. While there’s little to nothing that can be said on that front, it’s been made clear that we won’t be talking about Halo’s next major title for quite some time. And no, that doesn’t mean Gamescom. Or PAX. Trust us, when we’re ready to begin pulling back that proverbial curtain, you’ll know. It won’t be soon."
The part where they reference 'old-made-new' games is something that Spencer suggested himself, but 343i isn't will to confirm. It could be a Xbox One X enhanced Master Chief Collection or it could be the fan requested Halo 3 Anniversary.