This is in-line with previous rumors, the 7nm Navi architecture will not be a successor to Vega but looks like a replacement for the Polaris lineup. Basically, you can expect a Radeon RX 680 in 2019, this product is believed to feature the Navi 10 GPU in combination with 8GB GDDR6 memory. TweakTown speculates that for $299-$399, you may get performance close to the GeForce GTX 1080 or even GTX 1080 Ti.
A more potent version of Navi may arrive in the 2020-2021 timeframe, with the 7nm Navi 20.