I don't consider anything that's pay-walled to be high quality. If I can't read it, it has no value to me.

What do you consider high-quality?

operative word: i.

A lot of search is searcher context sensitive, so I don't think automating this is unreasonable

If I continue to run into the same paywall, I would consider buying into it. If I bought content, I would want it to show up in search. I wouldnt know I want to buy it, if I dont run into it first.

Then Google should work on a way to connect your purchase with their system or give you ability to inform them you’ve purchased a subscription so that only you get to see search results from that paywalled website, and not others.

In that case they should return book results also, which are usually the highest quality.

a result is low quality if i can't view the content of it.