Scorpio's unveiling and pricing will probably be mostly in the form of a video/ad that's played for the first time at E3. I expect Phil Spencer to be on stage to drop some unreleased information regarding the console, and that's gonna take up the beginning of the Xbox E3 conference. Include a list of games that will be available with a Scorpio update come its release, and I think the unveiling could go well. I also expect a bit more in terms of hardware, the Xbox Design Lab might be expanded to include Elite controllers and consoles as well.
Next, we know what to expect for first party at this point:
-Crackdown 3
-State of Decay 2
-Forza 7
-Sea of Thieves
-Ashen
-Cuphead
-Probably Halo in some shape or form. Beta for 6? RPG? Halo Kart Racers? Halo Mega Blok's Evolved? Who can say...
I expect Cuphead to be available immediately following the E3 conference, or at least within the week, as a E3 showcase would serve to reignite the hype that's been lost while waiting for so long. Outside of that, New IP's or revival of older ones is kinda hard to gauge at this point, don't know what they might bring back or who might be working on it in the first place. I feel if they can deliver both, one AAA new IP and one old IP being bought back to life, id be satisfied.
Now in terms of third party marketing, I expect we will see Xbox get the rumored Assassins Creed project and possibly an upcoming Bethesda title, depending on how far along that is. Also, I would not be surprised to see Splinter Cell make an appearance, given the franchises history with the platform. I also expect to see a video contrasting many third party games performance on Xbox One, PC, and Scorpio. I also expect them to start showing off the rumored unified marketplace for W10 and Xbox that's suppose to be coming in the fall, but Gamescom seems like it would be a better fit, or perhaps that PC-focused E3 event they have been doing the past 2 years.
End the presentation with an "and one more thing"-style announcement of an OG Xbox collection, and I think it would be a killer show.