The Halo franchise has proven to be in capable hands with 343 Industries, so it makes sense that they would produce games outside of the main Halo canon. That’s apparently what’s happening right now, as 343 is looking to hire a new Creative Director to deliver a “groundbreaking new AAA entertainment experience set in the Halo universe”
The wording clearly rules out a main-series entry in the series, and the word “new” seems to suggest it’s not a continuation of a previous spin-off like ODST. While it could certainly be a new Halo Wars, the vague wording leads us to believe it’s an entirely new franchise. Whatever it is, it’s clear 343 is working on a Halo game that’s not Halo 5.