The best place I've found is Ruben Verborgh's blog (he's a researcher who's affiliated with Solid). For example here's a nice post which goes into more detail on the ideas behind Solid:
https://ruben.verborgh.org/blog/2017/12/20/paradigm-shifts-f...
2) In terms of applications, I'd personally like to see more of a focus on productivity applications, rather than so much focus on social media. Better interop between cloud SaaS apps would be valuable to businesses and professionals, and would sidestep many thorny challenges like decentralized moderation.
As a concrete starting point: what if I could store my Google Docs text files on my own storage layer, and edit them in realtime using a variety of editor apps? This would resemble my ability to edit a .txt file on my computer in vim or TextEdit, but would port that metaphor to the world of modern online collaboration.
Here's a short Twitter thread I wrote on this topic:
https://twitter.com/geoffreylitt/status/1355255162626068482
3) I'm very curious to see more incremental paths from the current web to a decentralized approach. For example, what if we could start annotating existing websites with private data and sharing those annotations P2P, rather than starting over from scratch?
I've explored this a bit with my Wildcard project, where users can store annotations in a "spreadsheet" that is linked to a web page: