They'd need to support a second graphics API, which is certainly non-trivial. The licensing permits anyone to do the work themselves if it's that big of an interest, though.
The macOS backend can probably use OpenGL as of now, it's deprecated but still there (and will probably remain for a long time because of legacy applications that cannot abandon it, hell even they added M1 chip support for it!). And if things aren't rosy then you can probably migrate to ANGLE (implementation of OpenGL ES on the Metal API), which should be pretty reliable since Chrome and Safari are already using it for WebGL support.