While the need for PCI-Express 4.0 seems a bit redundant and far-fetched for any near future graphics card it now looks like it that the 7nm Vega20 that was announced on Computex, might be PCIe 4.0 ...
The ME is data stored in your BIOS ROM and in your system RAM that is protected from the OS by hardware, so side channel attacks are an obvious method. Those don't rely on anything but hardware flaws ...