This is admittedly a niche request.
Since I use Taskpaper more as an outliner/structured text editor, it would be nice if there was a line-width feature. Ideally I’d want no line to be no longer than 65 characters, or so, but to have that depend on the line’s actual length. I have not idea how that would work in the real universe. I’d be happy with a setting or a slider that brings the word wrapping nearer than the side of the window.
Related to this is being able to enable the text to be centered in the editor window. So that you could, in effect, turn off the sidebar and use Taskpaper as a full-screen editor without the text going from one side of the screen to the other.