Dell used to make mini-PCIe video card on some of their laptops. No idea if they still do. I know on my Inspiron E1705 I had in 2006, I could swap the video card for a new one provided I could actually source a new one. I don't know anyone selling mini-PCIe cards outside of eBay, but it is possible to make a modular laptop.

Newegg actually sells barebone laptop kits.