the biggest missed opportunity with SLI/NVLink was not using the high speed shared memory bus to enable the use of a large number of display outputs as if they were all connected to one GPU.
it wasn't until I started trying to daily-drive 5 or 6 monitors that I appreciated just how slow it is for the desktop compositor to move the framebuffer between cards, and how many stutters and other annoyances it causes when moving windows between screens.