Lovely to see this come up again. It's really a great time to promote Solid, with the evidence of shady practices at the big corporations mounting, I know lots of folk would like a way to reclaim some of their data.

That said, I feel like the big starting point for Solid is exfiltration/syncing of data between services, and that appears to be missing, for the most part.

Give folk an app that will pull their music preferences from Spotify, and let them try out Amazon or Apple music with the same collection. It's a very simple data set, and a fairly common and comprehensible use case.

Doing photos from Facebook/Instagram/Twitter/etc would be a bigger lift, but not too much different in concept, and I think very compelling in terms of selling the value of the service.