I think a far better approach is to just self-host your own applications, instead of just your data like a SOLID pod. Several solutions assist with this with varying levels of security isolation and open sourceness.
I use and contribute to Sandstorm.io, but also on the open source side there is also YunoHost, and on the proprietary side is Cloudron and Umbrel.
Self-hosted applications can still be closed source, but hosting them locally means you can monitor their behavior, and they should continue to work even if the developer shuts down and abandons it.
Selfhosting everything yourself is not realistic for the majority of users. And even experts who have the time, money and expertise, can't selfhost everything, after all at some point they must exchange data and trust others work. I mean, just take this forum. How would you selfhost this place which needs a centralized power which upholds order? How would you realize a good moderation and trustable voting on a dezentralized forum, with sane solutions? Sure you could decentralize this all and play blockshit-bingo, for a high price. But until we have a true dang-ai, forget about the quality of moderation. And this is just for a simple text-forum, let's not talk about youtube or the like... That's the point were solutions like solid make sense. Places where centralization is unavoidable, but also places were people are to lazy or "poor" to use other solutions, thus a compromise for the real world.
I use and contribute to Sandstorm.io, but also on the open source side there is also YunoHost, and on the proprietary side is Cloudron and Umbrel.
Self-hosted applications can still be closed source, but hosting them locally means you can monitor their behavior, and they should continue to work even if the developer shuts down and abandons it.