If it’s not true then you are actually removing the only major benefit of upgradability all together. Just get what’s available today since it’s fast enough and will be for some time.
I was saying that the Blackmagic eGPU in an upgradeable form factor would mean that you get a 200-300 $ (or something like that) GPU enclosure with some electronics in it (Thunderbolt hub, power supply etc.). Then you stick a current GPU into it. This would make sense because GPU replacement cycles are much shorter than the interconnect upgrade cycle. That's why I said that most applications are still fine today with the over ten year old PCIe 2.0.
So just to reiterate: PCIe bus speed is simply not a limiting factor for the overwhelming majority of GPU applications.