Hey, I finally got around watching the video and the idea is pretty cool :).
I guess the main challenge here is to make applications using different protocols work together, though that’s probably not possible at the moment. But, if this works well for all the protocols involved, I think it’s pretty cool already!
However, having seen ActivityPods, I wonder if that implementation using a graph database is conforming with the Solid Protocol… Other than login in, have you tried using existing Solid Applications? I did try to use ActivityPods a while ago with one of my apps, and I ran into a lot of problems trying to make it work. I think one of the main reasons why that happens is precisely that they use a graph database, instead of a document-centric store like the Solid Protocol expects. I’m sure there’s also some issues with making ActivityPub work together with Solid, but I don’t think that should be the main problem.
In case you’re interested, I documented my issues with ActivityPods a while ago, and there’s also been a couple of threads in this forum talking about bridging the two protocols (not sure I’ve seen anyone doing it with ATProto, though!): Integrating ActivityPub within Solid specs