Wayland out of the box?
Will give Fedora 27 a go this evening and see...
Wayland, or rather gnome-shell, seems to do EDID detection a bit differently than Xorg. Getting a higher quality DisplayPort cable fixed it for me. The earlier cable did OK at 30Hz but freaked out trying for 60 Hz. X11 must retry more times, because it would usually manage to make it work for a while on the bad cable, although it still could randomly flicker off and reset the connection.
Additionally, some laptops have external displays wired to Nvidia, making it impossible to use intel-only graphics with external displays.