After which you'd have to load 8Gb from disk/SSD in under 1 second...

No, you don't. You need to load kernel space, and then demand page in the rest as it's being accessed.

I wonder if there are any disk suspend systems that are smart enough to tie into the VM system... instead of a specific monolithic RAM-sized suspend file, just flush everything to virtual memory on suspend, and on awake only restore the minimum needed for the OS and accounting, then start swapping everything else in lazily as the user needs it (or in advance in the background if the user is idle)

Given that the disk is several orders of magnitude slower that the RAM, lazily re-loading pages from the disk to the memory can induce very visible and annoying loading delays everywhere (e.g. change tab in browser takes 3 sec).

I'd rather wait 10 extra second than having a slow computer for the next 10 minutes.

Or you could go for the hybrid, of having 10 seconds of reduced performance while the system keeps aggressively loading pages.

Linux does approximately this.

If you need 8G of resident memory to have the apps you want running then you need 8G... no shortcuts. That is a pretty high figure, though. Afaik things like disk caches aren't restored during a suspend/resume.