Xbox Scarlett could have a real effect on gaming PC sales. For a lot of people, why would they pick a gaming PC instead of an Xbox Scarlett? Both will have mouse and keyboard support*, both will have crazy fast SSD’s, and the vast majority of people won’t have any complaints about Scarlett’s graphics or power. You won’t have to deal with any of the BS you do with gaming PC’s, just plug into the TV/monitor and play. I just can’t think of a reason it would be worth choosing a gaming PC instead of an Xbox Scarlett, gaming PC’s in the same price range won’t have any big advantages over the Xbox Scarlett.
*I’ve read that a lot of Scarlett games will be designed with keyboard and mouse support in mind from the beginning, unlike Xbox One games.