Turns out a lot of Halo games have been pitched to Microsoft and 343 over the years, with many of them never seeing the light of day. Some of these 3o-odd pitches looked to bring back Halo's ODST unit in multiple forms, but most never made it past the initial planning stage.
RELATED LINKS:
Lego Halo is built by a single dev, has fully playable deathmatches
The next Halo is finally on the way, and that's for the best
Mysterious Halo battle royale is dead, allegedly