There is no exclusivity deal.
They simply dont have the resources to do multiple ports.
Sony helps so they automatically included in the first platform to get the game.
If MS willing to pay, they will get it too. But they dont.
The FAQ is there in the kickstarter. Clearly stated no plan for other platforms but no mention with exclusivity.
Sony is clear too with their saying "coming to playstation first"
Both are easy to undertand that the game can be released on other consoles provided they have the resources.
(Unlike RoTR exclusive | Winter 2015)
A deal to "release on PlayStation first on consoles" is an exclusivity deal, regardless of what the window may be. It doesn't rule out games being ported to other platforms at some point, but I highly doubt MS can right now go to Suzuki and say "let's do it for X1 day one as well, we'll help". The only real difference with something like Tomb Raider is the lack of clarity (even though we know what the deal is there, regardless of them being reluctant to state it). Shenmue III is in a space similar to something like No Man's Sky. Sure the devs can think about other potential platforms, but there's probably not any chance of them releasing to those platofrms day 1 regardless of what other resources they may find. This is standard practice, and as far as I'm aware, there isn't any examples of this not holding true for a deal such as this.