He spent a lot of time looking at my mum's (questionable) books and making notes.
I've thought about that a lot over the last 20 years. How much insight you can gain from someones bookshelf.
I'm now addicted to it, where ever I go. Feels rude and invasive though, so I try not to be too obvious
There is missing metadata in that approach just like there is missing metadata in the bookshelf approach.
What we need is a way to make filter bubbles and echo chambers fungible. Like, we should be able to alter our user session to that of our contact's, with their consent. Transmit their whole data-broker profile to our computer and look at it. Or browse the internet and social networks as if you had their session, just to see how search results are different, how news headlines are different, which articles are shared to them, what their stories are reinforcing.
That will be even more insightful than what your world used to be like.
People change a lot over time; I don’t judge people on what they have on their bookshelf, but it definitely provides fast context for their worldview, providing background for who they are today and how their opinions developed. It provides an immediate jumping off point to discuss common interests and ideas.
There’s nothing better for this purpose.