They can treat as a new console regarding presentation. Show some tech demos, announce a few games that showcase the hardware (a perfect example would be the new Forza, it wouldn't be a E3 surprise anyway).
Show a glimpse of the new UI (Scorpio will come with Redstone 3) and some new features. Talk about the exclusive features the console might have (like longer game dvr times).
Show some announced games running better on Scorpio, provide a list of games that will be updated to support Scorpio. Perhaps even have a bombshell in that area (like all xbone games will see a resolution boost on Scorpio without a patch).
Anyway, there's plenty they could show of the console that wouldn't fit e3, gives them an opportunity to talk about the future in general like updates, and give e3 more time to focus on new games.