So this thing exist : http://www.banggood.com/Mini-PCI-E-Version-V8_0-EXP-GDC-Beast-Laptop-External-Independent-Video-Card-Dock-p-1011222.html
The MiniPCIe slot in Librem 15 is being used for Wifi card.
I’ll just use a USB wifi card, and plug this adaptor into it instead.
Let’s see if Librem 15 can use eGPU (external GPU) this way ! 
cheers, HS