There is a loooog thread on the official forum on open source for Obsidian app: forum.obsidian.md/t/…/1515
IMO the best approach would be for them to make the promise, that they’ll open source the code if they become unprofitable or uninterested in further developing ObsidianMD and then leave. In that case, the community has a fully open source stack.
I am aware, that Obsidian is closed source, I try to keep the number of non-compliant uses of markdown minimal. While I use quite many plugins, I am aware, that the plugins being open source removes the risk a bit.