Intel's reference designs for thunderbolt are behind NDAs so it's a pain in the ass to implement on a PCB and I don't think the controllers themselves (or their

Intel's reference designs for thunderbolt are behind NDAs so it's a pain in the ass to implement on a PCB and I don't think the controllers themselves (or their datasheets) are easily sourceable either. The Pi foundation has probably got the pull to do it but it would take quite a bit of effort since it would make the Pi an easily available competing reference design, possibly running into internal politics at Intel.