Good question, so we checked. Of the 136 domains on p=none, 20 (about 15%) publish no rua address at all, so their aggregate reports go nowhere. The other 116 do send reports somewhere, though from DNS alone there's no way to tell whether anyone reads them.
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Proof Over Promises.
The 13.6% sitting on p=none is the number I would chase, since many of those likely moved there for the 2024 Google and Yahoo rule and never looked at the rua reports again. Would be interesting to see how many of the p=none domains also have no rua address at all, which means nobody is even monitoring.