I have a feeling that there will be a few exclusive 1st party games revealed at E3 this year, with a release date of holiday 2016.
a) Phil Spencer has said repeatedly that he wants to greatly shorten the time between 'reveal' & 'release'
b) Scorpio releases in the last quarter of 2016
c) It's been said that Scorpio will be treated a bit more like a traditional 'new' console, with 'launch' games (even though they will obviously be compatible with Xbox One).
d) Spencer has said that there will probably be a Scorpio reveal before E3, since E3 is focused more on 'games' rather than 'hardware'
Here are my guesses for the games that will be released within the launch 'window' of the Scorpio release:
Sea of Thieves
Crackdown 3
Forza 7
Unannounced Dead Rising 4 stand alone DLC (like Super Ultra)
Unannounced 3rd-party-made Rare IP game, published by MS (ie. Battletoads, $20-$30)
Unannounced smaller 3rd-party exclusive game, published by MS (Like Recore)
Minecraft update, adds mod support + realms (possible Scorpio exclusive stuff for mods)
and my pie-in-the-sky hope is something like Sunset Overdrive 2 (but I think Ryse 2 is far more likely right now)
Other games, like State of Decay 2 and the remasters of Voodoo Vince/Phantum Dust will come out, but I doubt they will be in the 'Scorpio launch' window.
Also, keep in mind that when Spencer refers to 'first-party', he considers any third-party game published by Microsoft (exclusive to Xbox and/or Win 10) a first-party game. So Sunset Overdrive and Cuphead for example are 'first-party' games in his eyes.