alt Hacker NewsI think on a technical level you're right, but you need to run two of them and they'd need a custom design like so:
https://i.ebayimg.com/images/g/RQIAAOSwxKFoTHe3/s-l1200.jpg
For what is essentially a dead-end technology, I'm somewhat doubtful people would have bought it (since the second GPU is going to be idle and add to the cost massively).
the CPU being upgraded would have been much easier though I think.
That's the crux, I think.
Apple even in 2017 had the money and engineering resources to update or replace their flagship computer - whether with a small update to Skylake & Polaris and/or a return to a cheesegrater design as they did in 2019.
But they chose not to. They let their flagship computer rot for over 2000 days.