This just tweeted:

This just in from Phil himself said the following in response to Killer Instinct which was announced after gears for PC:

"And it's the beginning for us."

50-50 chance.

If it does then there is no reason to buy an Xbox One.

XBox will still probably have large exclusivity windows on the Halo games, but yeah I don't really see the harm in making a PC port like 12 months after an XBox release.

If Halo 5 came to PC...don't even want to say anything

I'd lose a good reason to own an Xbox One, that's for sure.

Maybe like a couple years after they come out on Xbox 1

it have to be realy cheap to be a hit. they have to overcome some problems they had with pc gamers and their sellinglattforms in the past, and the collection has no real market on the pc. its way to casual for core pc gamers and it has no mod support, no fanbase, and is just to weak for the market.
it has to beat doom and ut15 and well, thats not gonna happen.

I'd say that it is just a matter of time.

Looks like Phil is ready for more:

Spencer did confirm that Killer Instinct is coming to the PC and will support cross-platform play with Xbox. "I think it's a great franchise for us. We've seen fighting games do very well. And it's the beginning for us.