It would be useful to be able to create a table of contents for projects which would appear as a sidebar just below the "project photo" if one has been set. There are several things that could be implemented to make this happen, each of which would be useful in its own right.
(1) There would be a template that automatically creates a table of contents based on the headers. So placing {{TOC}} in the project overview markup might insert an automatically generated table of contents as a sidebar, for example. Even if there isn't an existing template system, this one special "template" might be implemented like the project photo system, as a special feature for creating an automatic sidebar.
(2) A requirement for this would be: Headings would automatically generate HTML id attributes, like they do in MediaWiki. Right now there is no way to create links to sections within a project overview text. The simplest and most useful such links would be to section headings, which would probably also be relatively easy to implement.
(3) A component that might be part of this is: There would be a way to create a floating right sidebar, which MediaWiki implements with templates {{templatename}} like the sidebar template {{Sidebar}} that is the basis for many types of sidebar. Are templates already implemented in some form? What ones that project editors can use within their project overview markup text?