I dont see thunderbolt taking on, with intel proprietary rights on it, idk, never have i seen a motherboard with it worth the extra $$$, then again i dont have need for such interface.
I can see it useful for laptops though, where you could be having a ultraportable and just hook it to an external PSU + eGPU for gaming, at home, etc. There are tons of people already doing it in other formats having success, NBR e-GPU (External Graphics) Discussion
. You probably could ask your questions there, since there are poeple that do what you want to do, just in laptops.
Personally i dont see my self changing toward external gpu on a desktop, i love having all in one box. Tech that have me excited for the short run are Sata Express, DDR4, PCIe 4.0, and to get a 4k monitor....