Users online have confirmed, or at least provided strong evidence that through the Infinite footage released by 343 that the Prometheans are indeed in Halo Infinite.
When Escharum (a very weird name to type and speak btw) spoke of the “Harbinger and the Banished working together”, users quickly found that in Halo 5 Warzone when you kill Prometheans it says “You killed a Harbinger.”
So yes, backstreets back alright! We can’t have a 343 Halo game without them putting “their stamp” on the franchise, to the detriment of features/enemies fans actually want. We haven’t took down a scarab since Halo 3… yikes. But we have battled waves of robots! (Yes I know they are not robots, but they certainly come off like such to players)
I guess this may also shed light on whether or not The Flood is in Halo Infinite. With the cartoony/Mega Bloks aesthetic of the game so far I think they would have a hard time fitting in. Now that we know UNSC, Banished and Prometheans are in the game, having a 4th faction may complicate things and dilute the storytelling elements of the core campaign.
The interesting thing is now that we know Infinite is meant to be “platform for the next 10 years of Halo”, and that no sequel is planned, I imagine we could eventually see The Flood in Infinite drip fed to us through DLC, rather than being in the “next Halo game.”