Currently, custom modelines are only supported on an Xorg session using xrandr, or on Wayland by using a custom EDID. My request is to have support for adding custom modelines on-the-fly in Wayland sessions like what xrandr allows for.

This has several real world usecases, such as better support for CRT monitors and TVs, being able to overclock displays to output at a higher refresh rate than its EDID says it's compatible with, being able to control resolutions and refresh rates on displays that do not provide an EDID (like a 15KHz CRT TV when using adapters/converters), being able to use super resolutions (large horizontal resolutions with a smaller vertical resolution), and probably some other usecases as well (CRT SwitchRes being another example).