I think the most common (and worthwhile) use case that the current spec does support is
- a single introduction line, often ending with a colon (or not with a period; at least in English),
- followed by multiple list items (cf. Should single element lists be supported?),
- which are usually all single-line and therefore constitute a non-nested, tight list,
- followed by a blank line like there would have been after the paragraph without the list.
<!-- blank line -->
Introduction:
* List item
* List item
<!-- blank line -->
I wonder if it was enough to require two or more of these characteristics.
I also wonder whether such lists should be a part (i.e. a child node) of the paragraph if the output format supports that (HTML does not).
Btw.: The introduction line is usually not a list caption or list heading, so it wouldn’t help to have markup for that. Elsewhere it would (e.g. 7 #).