Opensourcing could be an option in future. For now, we would like to see how people adapt it to their needs. Because it's quite untraditional tool.
There might be a Github like business model there: a business that improves upon an existing tool and grows by expanding the market.
Now if you can format branches in Markdown, drag & drop images and other files, keep documentation, study notes, code examples and simultaneously write information with a few more colleagues - that's quite useful I think.
Next version of Markdown Tree should support various embeds like: Youtube, codepen.io, Google maps, etc. That would allow to have a nice workspace for various kinds of tasks. And only web apps are capable of it too.
In a sense, it captures one of the *nix principles of outputting to conventional interfaces...it makes things rather than being an end in itself. If it had collaboration, people might use it to collaborate on writing a program or a web-page.