Obsidian is free to use, and they make their money from offering additional sync-service and good will of the users. I don't think open source would impact it much. Though, it would bear the risk of a hostile fork, maybe to include a free to sync or something. I mean the obsidian-devs have some bad history on that front.
But at least they should give some guarantee to Open Source it if there were no significant update in a while, similar to how Qt and KDE have their agreement. Or at least they should make the source available, so people can contribute or move away easier in case of problems.
