Nobody knows except Robot Entertainment. Bungie shut down Ensemble Studios because they messed up Halo Wars, by putting in Brutes and Scarabs that the Covenant didn't even have in that era, so, probably no Halo Wars 2.
I thought Microsoft shut down Ensemble, as they owned it and there was a funding issue which preventing Ensemble from further existing. Either way, Robot Entertainment do not seem capable of developing a new game. They lost a lot of staff from Ensemble.