On Reddit, a recent AMA thread picked up the details where the community director of 343 went over a couple of pressing questions regarding the Master Chief collection on PC. The bulk of the questions regarding Halo Reach were answered by the user until someone popped the Q about Halo 5. Brian, the rep from 343, states:
“Our focus is bringing MCC and Reach to PC, there are no current plans to bring over Halo 5.”
Brian is saying that they don’t have plans, but this isn’t confirmed. However, at this point, it doesn’t seem like they’re planning to include the game.