IMHO, the introduction of a new element needs to be supported by a certain amount of use cases. And as discussed above, we still haven't seen an use case which really shows the necessity of such a new element.
A list isn't likely to just exist on its own purposelessly in a document; its existence surely is accompanied by some context that can explain its purpose. In such a case, a list heading is redundant.
If some of you really want list heading so eagerly, I personally would suggest resorting to CSS generated content instead. For example:
content: "Noble gases";
This approach of relying on CSS generated content for semantics is inspired by @SteveF, who is a supporter of the said approach. Although I personally disagree with the said approach, it's still better than seeing a redundant element (imo) being introduced into HTML.