With Halo: Reach being released for Halo: The Master Chief Collection, Halo 5: Guardians is pretty much the only regular Halo game that isn't included in the massive collection as 343 Industries prepares to publish the series on PC. And it seems like it will stay that way, for now at least.
343 Industries community manager Brian Jarrard hosted an AMA on Reddit over the weekend and naturally one of the questions he was asked was whether we should expect Halo 5: Guardians to show up in The Master Chief Collection and, therefore, on PC, to which he replied:
"Our focus is bringing MCC and Reach to PC, there are no current plans to bring over Halo 5," he wrote, dashing our hopes of a complete saga on PC in the process.
This could, of course, change in the future as Halo: Reach was also at one time a game that they didn't plan to include either. However, don't expect Halo 5: Guardians to be added anytime soon, even if it doesn't sound too farfetched that it might happen one day. We live in hope.