It's not quite as easy, because if you're using, say, Intel graphics, you get maybe two clock signals, so you'd likely have to use your own. (Although you said

It's not quite as easy, because if you're using, say, Intel graphics, you get maybe two clock signals, so you'd likely have to use your own. (Although you said AMD and discrete mobile GPUs :-)) In addition, the laptops that use eDP (Chromebook Pixel, which uses https://www.revo-sys.com/prodimages/LCD-Display-Panel/LG-12.9-LP129QE1-SPA1-LVDS-2560-1600-400-NITS.pdf https://www.revo-sys.com/prodimages/LCD-Display-Panel/LG-12....) are using those lanes (and probably the aux lanes) for the primary touchscreen display. The external display interface is going to be pretty vanilla (mini-DP IIRC).