As long as it's some automated signal, the User-Agent can use any logic it wants to send it without cooperation. The specifics of how to send the signal don't have to be legislated. E.g. Firefox's Tracking Protection has a global default a site-specific overrides, so it's very likely that they would do the same for this or just combine those features.

Comission wanted that, Google lobbied hard to NOT have automatic sigal… go figure…