Why would they launch a successor to the current generation when there is no competition and no commercial pressure to do so? they own the market and sold more cards in the last quarter than ever before. it would not be good business, for Nvidia or their Stakeholders
The commercial pressure is that they can get people with 1080s to upgrade to something faster, or push those with Maxwell/Kepler to finally upgrade. They can also show an even stronger advantage over AMD.
However, Nvidia really have to release the 2080 in July-August time frame or not bother at all until 7nm is consumer ready next summer.