Yes. See https://github.com/aarch64-laptops/edk2/tree/dtbloader-app?t... for example.

It's a shame the DT approach encourages land fill of boards when the manufacturer stops providing updates.

Not necessarily. DT can be loaded separately from u-boot tree / kernel tree / dtoverlay file.

The DT should really be put in the firmware (e.g u-boot), same as ACPI on x86 is in the firmware (the bios/efi).

Then you wouldn't need a unique kernel/OS image. For devices that have u-boot in ROM the DT is usually there (fdt).