With the announcement and Beta of Catalina, it's time to accept reality. Apple and Nvidia seem bound to have effectively ended new Nvidia card support in 10.13.6.
This is sad for a number of reasons, Apple being bad guys is never nice. Guess they got tired of being embarrassed by higher benchmark scores and general love for Nvidia. In any case, unless there is a Blizzard in Hell, it appears that CUDA on Mac ends there too.
There could be a surprise yet, but as of right now, June of 2019, there is no path forward .