USGA Open venues get added in the year the venue hosts the US Open.
We don't have a way to anticipate the addition of any non-US Open courses, unless WGT says something.
WGT already had the 2016 US Open venue - Oakmont - and already has the 2019 US Open venue - Pebble Beach.
So Erin Hills gets added in 2017.
2018
Shinnecock Hills Golf Club
Southampton, N.Y.
2020
Winged Foot Golf Club
Mamaroneck, N.Y.
2021
Torrey Pines Golf Course
San Diego, Calif.
2022
The Country Club
Brookline, Mass.