Just to be clear: I will not subscribe to every single newspaper just because an article got linked on hn.

That's not a very good answer. Do you think one newspaper should allow you to read their work because you subscribe to another? If you don't want to subscribe just turn off the adblocker. They're giving you the choice.

Just to play devil's advocate, I wonder if it would be possible to sustain WaPo from Amazon's revenue stream, and what impacts that could have on ostensible and de facto journalistic integrity.

Not really addressing the heart of your question but WaPo is owned by Bezos and his holding company not Amazon. So they would not really have a great reason to siphon off Amazon's revenue stream.

1) WaPo is not owned by Amazon.

2) That would create a clear conflict of interest. This post is an example of what can happen when you have only one source of funding which you may need to criticize.

Jeff Bezos owns both Amazon and WaPo. The original comment went to sustaining WaPo on Amazon's revenue, not ownership. The conflict of interest already exists. Don't expect anything substantially critical of Bezos or Amazon from WaPo.

Amazon is not owned entirely by Bezos so he would have to justify using Amazon revenue to support WaPo to the rest of Amazon ownership. If Amazon owned WaPo that would be an easier thing to do in the same way Amazon may subsidize IMDb, Zappos or Whole Foods. In this case the distinction between the two matters. Just because the same person is in a similar position at both companies does not mean money can easily flow beteeen them. This is the same reason the WaPo is not a tax shelter for Amazon.