For more context, if I recall correctly, phh is the first person outside of Google to figure out this Generic System Image thing, and has been tinkering around Project Treble ever since.
(And I just learned about the GSI image for Pixel 1/2, thanks for that!)
GSI isn't specifically for Pixel 1 and 2, but they can use those, just like every other device whose OEM have abandonned them, since it is a generic image.
(And I just learned about the GSI image for Pixel 1/2, thanks for that!)