I am getting an EXP GDC soon ($54 from a US seller), these are x1 bandwidth. Mini pci-e swap out the wireless card and use a USB wifi, or an expresscard setup still on x1 link. Even Thunderbolt 3 and USB-C will be around x4 max. Getting the dell da-2 220W ($11 ebay) power brick to avoid some of the ATX psu clutter you see on youtube. Was planning to hack a 203W xbox 360 psu until I found the dell.
I have a dell inspiron sandy bridge with 525m, wanting to see how much of an improvement a 750ti will make before trying anything larger. My laptop uses optimus, so even the egpu will display through the internal lcd. May need to modify the inf of the mobile driver to install the desktop GPU with optimus.
Between x1 link and optimus frame buffer copy to internal display expect at least a 10% drop from normal desktop x16 use. Even so can breath some life into a laptop, use the laptop like normal portable then hook up the dock and gpu to game when home.
Some manufacturers use a white list for their expansion cards and anything not on the list will not work without modding the bios.