Flush in the dark
Wow, how can you design a toilet where you cannot flush in the dark?
This is a small thing. But if you think about it, a toilet where there's 4 buttons, close to each other, no structure or braille to guide you. How stupid is that. However, this is a really easy problem to solve. Just take a couple of the small self-adhesive rubber knobs, apply them, and it's now easy to flush in the dark :-)