Is it possible to add a PCI express lane to a raspberry pi for adding a GPU?
Apples and oranges my friend. Start here:
https://en.wikipedia.org/wiki/PCI_Express
then look at those power requirements. For the same reason you can't add a gpu on a phone you can't add it to the Pi.
I'm pretty sure The BMC2835 SoC and up don't support PCI-E bus communication, so even with enough power it wouldn't work.
