mask-border has the potential to reshape the web
You might ask, but what about corner-shape?
corner-shape is a good easy alternative for designers who does not have time to design arbitrary corner shapes
mask-border however gives designers the possibility to design arbitrary shaped corners, this can help with creating unique custom branding, which results in a more fun varied web
mask-border also gives the ability to texture background & border, which gives designers even more tools to create interesting branding