Some of the other wikis I have used have had the possibility to use an external editor to edit page contents.
I see that there used to be a WebDAV server in xwiki, but this is now being orphaned from the core.
What other possibility is available to edit content with an editor like vim or emacs?
Indeed the WebDAV support is not embedded and not supported anymore by the core team. Now it might still work if you install it (at least it was working well AFAIK when we moved it to contrib).
Except for this there is nothing out of the box to edit directly with vim or emacs AFAIK. We only concentrate on XWiki REST API now.