Microsoft could end up bringing games like The Master Chief Collection to the Epic Games Store, but don't expect any kind of time-exclusivity deals.
Right now Epic Games has one tactic: to keep as many games off of Steam as possible. The idea is to starve Steam out in a war of attrition, all while claiming to benefit gamers and developers by forcing Steam to change. Epic wins indie devs and publishers over with big cash advances and the 88-12 revenue split, and big names like Deep Silver, Take-Two, and Ubisoft all signed up. But big players like Microsoft won't play by these rules, and they don't care about timed-exclusivity deals. They care about maximizing exposure and game sales.
On Twitch, Xbox General Manager of Marketing Aaron Greenberg says Xbox games could one day show up on the Epic Store, but not as exclusives. The whole idea is to expand the playerbase, not restrict them with exclusivity. "Xbox games on the Epic Store? We're open. We're saying if somebody wants to offer we'd be happy to work with them. The key there would be is that we want to enable a broader connected community and we'd do it in a way that puts the player as the priority over the business."
This makes perfect sense for Microsoft.
The company is all about live services, engagement, and monetization, a synergistic three-part wheelhouse that thrives on huge playerbases and accessibility. The more people who can buy your game, the more people who can play your game (and consequently pay over time via microtransactions, subscriptions, and other monetization).
It'd be foolish for Microsoft to sign an exclusivity deal with the Epic Games Store for any game, especially huge AAA titles. There's a big advantage to bringing your game to Steam, namely its huge 80 million monthly active userbase. Microsoft wants its games everywhere, including the cloud.
So unless Epic changes its ways, I foresee Xbox games only showing up on Steam and the Windows Store when it comes to PC ports. Maybe that's a good thing...but then again, The Master Chief Collection on EGS would be a huge win for Epic.