Shortly on the heels of unveiling the Quadro RTX cards at SIGGRAPH 2018, NVIDIA released a new teaser video for the upcoming 'GeForce Gaming Celebration' event. The teaser drops quite a few hints, which indicate that the upcoming GeForce cards will indeed have an RTX 20xx nomenclature.
https://www.notebookcheck.net/NVIDIA-teaser-video-almost-confirms-the-GeForce-RTX-20xx-nomenclature.323004.0.html