So I've installed Ubuntu 17.10 on an external SSD and had it boot on my MacBook Pro A1706 (late 2016), works like a charm (installed the keyboard/touchbar module).
I have an external ThunderBolt 3 (USB type C) SSD drive. When I connect it, Ubuntu doesn't recognize it. lspci shows Thunderbolt is available. When connecting the drive to MacOS, it works perfectly.