Thinking about cats… they could do paw strokes in eight directions, and you can tell where it starts because the ink is thicker there. Then you could make those short and long, 16. You can add a hook in either direction at either end, 64. It would be pretty tedious for them, I think, so it would probably be phonetic, and they’d lean on shorthand.

I don´t know about the keyboard; my cat has no problems using mine.