Yes, Solid comprises open specifications and anyone can implement it. The open source implementation that sees most development atm is https://github.com/solid/community-server, which is nearing a 1.0 release.

Perhaps so. I don't know the details. I was operating under the assumption that the parent comment was correct in its accusation that there was no self-hosting option.

It doesn't matter in the aggregate if there is a self-hosting option if only the tech-savvy can use it.