I find the whole thing to be rather confusing. It's much too technical. Also it partially mixes the concept of ToC with that of a structure editor. It has some widgets on the ToC (add template, add content, change order) and others inside the editor (Add param, del param, del template). This is terribly inconsistent. And makes you having to scan the screen too much.
Also by default it tries to introduce you to the concept of chained templates ( starttemplate, content, endtemplate ). Which is rather complex and often not even needed.
This needs serious work to make the usability much more consistent and predictable. I would take the following into account.
1: Make a decision. Is it a toc, or a structure editor ? If the latter, then put all structure controls in the structure editor. Otherwise avoid putting them in there.
2: By default, don't show the buttons for chained/wrapping templates. Instead, only add them if Parsoid assumes there is content wrapping happening. For new templates insertion, make an addition to templatedata "openedBy, closedBy", and only add the buttons if the template data says they are needed.
3: Keyboard control. I try tab key to move focus to the "Add template" button next to the field. Seems this is captured by the UI, so I cannot move focus that way. It seems I can only click the button. BAD... Also seems that the add button and the delete buttons do not have a :focus state. Or rather, it seems that buttons have focus state, but the focusable element is the <a> inside it, so it doesn't really work.
4: The layout of the params view.. I don't know how to do it better right now, but this needs work. too many lines/blocks, it's too cluttered. Do you need a double line separator if you have a heading ?