After a fruitful discussion in Discord today, we came up with a few ways we might be able to improve the interface to ManageWiki. The first couple have to do with discoverability -- unless you know the name of the extension you want, it's hard to find something useful.
Split the long extension list into multiple categories, so that similar functionality is grouped together (kind of akin to what Special:SpecialPages does). While it might be possible to get this from extension.json, this might end up with too many groups. We may want to choose a smaller group to be manually determined, like "User rights and moderation" "Wikicode functions" (parser functions), "Appearance", "Editing", Special Pages", "Other". The categories might be grouped into tabs or with ordinary headers; I'm fairly agnostic on this point. Next to each extension, load descriptionmsg from extension.json (or the translation files). The intent here is likely to be able to read what is not applicable before reading every page on Wikimedia. The save tab is a little weird. If it's at all possible, can we steal CSS from Special:Preferences? Similar functionality should look similar, and the MW design team did a fairly good job on "page with tabs and checkboxes".
- Stretch goal: configure extension variables from this screen, which also increases discoverability. If this is even possible, or a good idea.
Honestly you've done a really good job with ManageWiki, I'm just proposing to add a little more polish.