AMD are working[1][2] on a graphics card that includes a 1TB SSD, which appears to your application as having 1TB of RAM and then just swaps to the SSD. I would say that's a pretty good approach to enabling virtual memory on the GPU - you get really fast swapping and you don't tax the PCI bus and CPU with moving data to and from GPU RAM. No release date AFAIK sadly.

[1] https://www.amd.com/en-us/press-releases/Pages/amd-radeon-pr...

[2] https://www.youtube.com/watch?v=g-8pMM2wV7k