Taking to Reddit
to respond to fans, Halo developers 343 Industries noted that when it comes to E3 next month "we'll have a little something at E3 but it's not related to the next major entry in the franchise." Which means we shouldn't expect to see a Halo 6 teaser. At least, according to this. As to what it could be, who knows, and the little something in question could be a potential Windows 10 version of Halo 5 or even the Halo: The Master Chief Collection.
Both would be awesome, but odds are it might just be additional content for Halo 5. On a separate note, in relation to Halo 5 feedback that criticised that game's story and its place in the canon, 343's Frank O'Connor noted that the studio has taken that on board. And in the process have come to the realisation that it needed more Master Chief.