Yolo Flamarkt will be open-source. It's already on GitHub, but I don't recommend anyone trying to install it just yet.
Some additional features might be released as paid extensions in the future. Other developers will be able to make plugins for Flamarkt as well.
Whether FreeFlarum will install it will be up to them.
The system requirements for the beta will probably rule out any sort of shared hosting though, because you'll need NodeJS and headless Chrome on the server to generate rich emails and PDFs.