What's wrong with good old notepad.exe and *.txt files? Notepad (nano, ed, other lightweight editors) has a quality that this doesn't: unstructured text. When writing I don't want to think about metadata, I just want to write, not think about titles, tags, etc. One could probably infer a title based on the first line. I think forcing structured data input is the wrong approach and it is better to use NLP or other methods of inference.
On a technical level, this seems to be a desktop web app which is overkill for a simple text editor. Compare its performance to notepad.exe which ran fine on machines from decades ago.