It could be very neat, but there are very few projects that would interested in it. localStorage is persistent enough for small hobby projects like this, and for something more serious you'd like to have some kind of backend DB anyway.
Not really. For instance, with TiddlyWiki you can run a local server and save everything on disk in a single html file. Jumping from localStorage to a DB means you go straight from "only in one browser" to having to deal with the overhead of a DB. A single text file has the advantage that you can drop it in a repo and have it version controlled or keep it in a Dropbox folder and use it on multiple computers/share it with others.
Oh I don't know. A serious dev team might want to be able to use their kanban on an airplane. An individual might want automated backup, while being able to code in a park or on the beach.
