None that I know of. Not sure the "blockchain" bit here matters much as I don't see how "proof of ownership" matter. More important is the fidelity of the data

None that I know of. Not sure the "blockchain" bit here matters much as I don't see how "proof of ownership" matter. More important is the fidelity of the data and that it can be packaged with other data. Companies like Kantar have representative panels (paid volunteers) with installed internet and tv monitoring, known household demographies, which fill in surveys, etc. Maybe worth having a look at things like that. Data under experimental conditions is still very valuable. The sample size need not be that big before it's useful when you're not having to guess at everything.