It is possible to modify the GeForce RTX 3070 to support 16 GB of VRAM, a YouTuber has discovered. Enabling support on the GA104 card requires setting 'strap' resistors to the correct values too, which all but confirms that NVIDIA had been developing an RTX 3070 SKU with 16 GB of VRAM, as had been suggested last year.
https://www.notebookcheck.net/NVIDIA-GeForce-RTX-3070-mod-confirms-that-there-was-a-16-GB-VRAM-configuration-in-development.526945.0.html