Frank O’Connor (Halo 5 franchise director) stated:

You know, Microsoft has made a huge commitment trying sort of… I think normalize the Windows experience across multiple platforms. You see the elements of Windows 10 are going to appear in Xbox and Cortana and stuff like that. There is plenty of chance that Halo 5 could appear on the PC. Nothing to announce at this point… you know, we developed the game on an Intel platform. It wouldn’t be the hardest thing in the world to move it to PC and take advantage of PC stuff. But nothing I announce today on this chat.

Source: http://www.dsogaming.com/news/halo-5-series-director-frank-oconnor-plenty-of-chance-that-halo-5-could-appear-on-the-pc/

I personally would like to see the trilogy first!  Mouse aiming, higher resolution, 120fps, and an improved FOV would easily become the ultimate Halo experience.  If they are serious about making Windows 10 a viable gaming platform, they will use Halo.

The following is one of the previous message regarding Halo for PC:

@Boogie2988 message received

— Larry Hryb, Gamer Emeritus 📱⌨️🖱️🎮 (@majornelson) June 17, 2015

Locked due to request by OP - PwerlvlAmy

Ka-pi96 said: Already posted.... twice http://gamrconnect.vgchartz.com/thread.php?id=209444&page=1 http://gamrconnect.vgchartz.com/thread.php?id=209452&page=1

Self reported.    How is this not a bigger deal? It got lost in the shuffle.