Silicon Graphics started to provide dedicated graphics terminals and workstations in the 80s. So the technology was definitely there, even for 3D.

In 1991, they put this technology on a PC expansion card with IrisVision.

So if this was possible for a full 3D-pipeline in 1991, for the simpler hardware needed for GUI acceleration that should have been possible a lot earlier.

The main problem earlier would have been fast enough access to the RAM, so I'd imagine a second card for video RAM (including DACs etc.) with a direct connection to the first card would have been a possible solution.

And the Xerox Alto had a framebuffer-based GUI back in 1973, with some assistance in the microcode. Though not on an expansion card.

So, very much possible, and somewhat based on reality (though not in this exact variant).

Silicon Graphics started to provide dedicated graphics terminals and workstations in the 80s. So the technology was definitely there, even for 3D.

In 1991, they put this technology on a PC expansion card with IrisVision.

So if this was possible for a full 3D-pipeline in 1991, for the simpler hardware needed for GUI acceleration that should have been possible a lot earlier.

The main problem earlier would have been fast enough access to the RAM, so I'd imagine a second card for video RAM (including DACs etc.) with a direct connection to the first card would have been a possible solution.

And the Xerox Alto had a framebuffer-based GUI back in 1973, with some assistance in the microcode. Though not on an expansion card.

So, very much possible, and somewhat based on reality (though not in this exact variant).