Not sure if I am the only one here thinking this, but this "Scorpio" console doesn't sound like a mid generation refresh to me. It sounds like a completely new platform.
I could be wrong, but if they are using the rumored stuff like Vega, HBM2, and Zen, then that would be a massive power gap between the current gen consoles.
Also with the rumored vr partnership with oculus rift....I'm fairly certain that vr would only be able to work on Scorpio.
And also, if they chose to present it a a whole new generation, they would be able to rebrand and avoid a lot of sales comparisons to the PS4 base as that would be considered last generation.
Obviously I don't know their plans myself, but given the rumors, this is what would make the most sense to me.