I'm planning on redesigning the TOC with the next release. The Google Docs version of a TOC is absolutely horrible at how it's implemented by Google, but it's automatic. Moving forward the TOC will be a manual process for the time being.
I foresee having the main TOC (at the beginning) being a general overview of the entire document. At the beginning of each section will be a more detailed TOC showing you what is located in that section.