I love FOSS and Obsidian is literally the only close-sourced software in my stack, but open source is not necessary to prevent enshittification, not if you have interoperability. As long as data is stored in md files, if the obsidian team makes bad moves people can pack up and migrate to logseq or other competitors. While the 3rd party plugins add enhancements that might bog down switching, many of those plugins are open source and could be ported.