PCI-e 4.0 will arrive in 2019, similar with HDMI 2.1. Will it be everywhere? No, not exactly but...
Intel will need to have it in the fall chipset revision in order to "answer" AMD, much like they have had to answer the Ryzen chips which continue to be some of the very finest in a decade. Once 4.0 is in and AMD then produces GPU's that utilize it, Intel will join in during 2020 with their discrete cards and of course NV will also need to be "in" just to be on the same page. Perhaps they will try, for a little while to extoll how the added lane bandwidth makes no difference. While that may be true, in "feature list" that most buyers only read, it won't matter. They'll need a revision to the 2xxx series in 12 months or less that at least takes account of 4.0. They may well add HDMI 2.1 as well since that too, is coming to market in a month and while it won't matter to everyone, it will matter to enough to be a desired feature.
10/7nm, PCI-e 4.0, and performance are all places where AMD used to follow and now others are forced to react to their leadership. It's not all encompassing but it's a nice balance that's good to see again.