It looks like this isn't open source. If this is supposed to be one's second brain, please at least consider using a time-bomb FOSS license. Something like: you're permitted to use Obsidian under Apache/MIT/GPL license either 7 years after a given release, or effective immediately in the event that Obsidian shuts down.
I guess we all have an incentive to make you go out of business then ;-)
On a more serious note: I see no issue with software being a service and costing money if it's built on a standard that leaves the data in the owners hands and in the owners own structures. I.e. Markdown files synced using infrastructure like OneDrive/Dropbox/whatever with some nice features on top of it and a nice UI can cost whatever and no one should complain. Because if that software goes away the data is in the owners hands and in a standardized format supported by many other tools.
That should be the preferred way we build software btw. And to take it to the next level we should create more general purpose (and standardized) database tools that are user friendly, treat them in similar fashion as files by syncing with user owned Infrastructure and we might just get to the point where more rigid data structures can be used in a similar manner as what I described above for files. That future would be great.
I too see no problem in a closed-source application so long as the data files are open. I like the IDE analogy here -- you can edit source code with a bunch of different tools. Some open, some closed. But the important thing is that the source code is readable by all of them.
Thanks for raising this. I couldn't imagine using anything like this without a serious guarantee that if development ever bogs down I'd still have some way to keep it working and up-to-date. Even if the founders honestly intend this to be the case, who is to say that the firm that buys them up feels similarly?