Well, PC is finally getting some Halo content that isn't going to be terrible *cough* Halo Spartan Assault *cough*, the Forge feature from Halo 5 is going to be released in mid-September. It will be free to play and will come with a 16-player multiplayer component that means that Halo MP will also be a thing officially.
The only thing is that you will need Windows 10 Anniversary edition to run the game which means if you missed out on the free upgrade, you'll have to buy it or not play at all. The system requirements are also out, you'll only need a 650 TI to run at minimum settings, but to run at 60fps 1080p, you'll need a GTX 970 with 12GB of RAM and an i5-3570k. To run at 4k you'll need a 980 TI and i7-4770k or equivalent.
Whatever happens, it should be fun and make for some interesting modded custom missions made in Forge mode and maybe a new Halo 5 competitive scene on PC in multiplayer.
Full System Requirements here