I'd love to see feature that allows for the editing of more than one mask at the same time. In particular, when doing lookdev work it's common to test out materials on various surfaces. Often I find I am adding and removing objects and faces from a mask while doing this.
Since it's generally a best practice to NOT have one material covering another on the same surface, I usually want to make sure that any area of a material that is not going to be visible in final maps masked out. It would therefore be super helpful to have the ability to automatically subtract from one mask by adding to another, or vice versa. This would be especially helpful when using the face and mesh fill tools.