Sony who at the moment are selling more each quarter than the Xbox One and Switch, i.e. they are the Market Leader. Why on earth would they take a gamble and release a new product when you're already doing nearly as good as you could be doing, theres only one way it could go, hint its not up, its either the same or worse.
Why would they do this? 2019 at the earliest, though I think it would be 2020