I think it might actually have more impact this way: it's not only information that's lacking, but public awareness of the law on beach access, deliberately mud

I think it might actually have more impact this way: it's not only information that's lacking, but public awareness of the law on beach access, deliberately muddied by some false information and low-level intimidation from homeowners. By both collecting the information and making an app with some fundraising publicity, they can try to target both angles. That said, I would like to see this information make its way into OpenStreetMap, if it isn't already. In addition to just mapping out the paths, OSM has tags for access rights.