I believe older, obsolete forms of musical notation used a diamond shape too, or something similar, if I'm not mistaken.Also, I believe guitarists who read sheet music have a note that's kind of a diamond shape, like a quarter note but instead of a circle on the note it's a diamond, I think that's for pinch harmonics or something. So that would complicate things for other musicians.Personally, I like the system we use now. Double sharps and double flats are not all that confusing once you understand them easily