Still going with 2019. 6 years is good enough for a normal gen going forward. Hell, the PS2 launched only 5 years after the PS1 came out. I think Sony was being honest about Pro being mid-gen, also. 3 years til Pro. 3 years til PS5.
And there's a reason Sony is going to do this. Like it or not, this is going to most likely be PS4's peak year. It'll at least be on par with last year, so ~18M sold-through. But, starting in 2018, we are going to start seeing a decline in sales, especially mid-late year. My guess is ~16M sold-through. Reason being that we will get a $199 PS4 this year, but I don't see it dropping much after this. $149 also isn't going to give the same boost $199 will. 2019 will see another drop, guessing ~14M sold-through.
This is the perfect time to launch a new console. As the interest in your console declines, you cause a resurgence of interest in it with new HW. Early adopters who are ready for a new gen will move on to the PS5. Those late adopters will grab a $149 PS4 or $249-$299 Pro. And those in between will stick with their own PS4s/Pros, and play the many cross-gen titles that will be launching for the next year or so. It'll also ensure that MS, if they are making a XB2, won't be able to get a headstart on next gen.
