Well, servers can also have software remote displays, display over ethernet or IPMI, or KVM switched displays. Digital signage may place the display many meters away from the computer in an outdoor electrical box, could well require a mosaic of displays over many ports to make a huge image, and can also be interactive through a large touchscreen or other sensors. Digital signage can sometimes also require pretty substantial graphics processing if the effective resolution is huge or if it’s highly reactive or interactive with many animations. Embedded devices can have irregularly shaped displays, weird interfaces, or again, multiple displays. Linux has excellent solutions for all of them, so I find it hard to believe that a remote PC environment connected through Thunderbolt would challenge it, barring a driver issue (which, again, would be Intel’s fault since Thunderbolt is proprietary to them, not a problem with Linux per se).