Is there any chance that when a new section is created, the edit summary anchor will automatically expand any templates used in the header? That way, it functions as a proper link when being accessed from the edit history...
Topic on Help talk:DiscussionTools
Sorry to be the bearer of bad news, but the answer appears to be 'no'. Imagine what would happen if {{infobox person}} got expanded in an edit summary.
not the summary itself, but the section anchor that is expanded between /**/. I don't think people regularly use infoboxen as section headers... is that even possible?
Yes, headers can contain anything that doesn’t contain literal newlines (except for those that are within <!--HTML comments-->, which are allowed even in headers) after expanding templates. Even infoboxes. The section anchor is the textual content of the infobox, for example
== {{#invoke:String|replace|{{Extension}}|
| }} ==
has the ID #MediaWiki_extensions_manual_Sandbox_Release_status:_unknown_MediaWiki_License_No_license_specified_Download_No_link_Translate_the_Sandbox_extension_if_it_is_available_at_translatewiki.net – not particularly short, but still well within the comment length limit.
I can easily imagine someone with a question about an infobox using {{Infobox person}} as a section heading, at least until they post the comment and realize the mistake. Consider this section at enwiki's Village pump (technical), in which a problem is reported with a citation template. If you edit the page, you'll see that the section heading includes nowiki tags.
It sounds like the goal is "Make the /* section heading */ links in the page history always work, even if people add weird or broken formatting in the section heading". Is that right?
that'd be about right, yeah :)
I think some work has been done on this in the past (i.e., it's not as broken as it used to be), but there is more to be done. Realistically, you might want to mark your calendar for the next Community Wishlist and propose it then.