I think this is unlikely. All of Apple Silicon is based on a unified memory architecture. GPUs and CPUs share the same, incredibly high-bandwidth memory. In fact, the GPUs CPUs in unified memory are all part of the same chip package.

Whereas All current PCI-E graphics cards include their memory on the card itself. Which means the CPU is having to copy data to, and from the external graphics card to do basic video operations.

In this interview on The Talk Show, John Ternus, vice president of Apple hardware, says he sees no way to incorporate external graphic cards into the Apple Silicon architecture (at 22:48)

https://youtu.be/DgLrBSQ6x7E