There's an underserved market in SF, too. I'd pay cash money for a regularly updated restroom finder.
Best of luck!
EDIT: どうもありがとう!
Just saw the Hirigana on the landing page. My Japanese partner and I have been lamenting the failure of public restroom availability compared to JP.
Heck, even compared to the US 2 decades ago when gas stations allowed public access to their restrooms.