They must be thinking of 'breakthrough experiences' that developers wouldn't be inspired to create without Scorpio, but will still run in some fashion on Xbone.
Then they don't need the Scorpio to promote it. Games are already being designed for PCs so if high end hardware was necessary to inspire those 'breakthrough experiences', then we already have it. Besides, where exactly do you think early games making full use of Scorpio would be developed? It'll be on PCs since Scorpio doesn't exist yet.
I think the more likely explanation for the early Scorpio announcement is to try to freeze the waters ahead of Sony's Neo. Microsoft doesn't have a counter for that ready any time soon so they are doing the only thing they can do. They are announcing a more powerful Scorpio to be released at a later date in the hopes that some potential Neo buyers will wait once it is released.
Also Microsoft already got stuck with the "less powerful console" label with the XB1 which is exactly contrary to their previous positioning of the Xbox brand. They need to erase that mistake as soon as possible. It doesn't matter that they don't actually have a console able to do that yet. If Microsoft didn't announce the Scorpio then the Xbox One S would be left hanging out there to compete against the Neo, and once again the Xbox would be viewed as the less powerful console.
Games can be written to scale based on the hardware its running on, you know.
So what. A scaling game isn't exactly what I'd call a 'breakthrough experience' now is it?