@scottjenson @julian@activitypub.space Apparently the process of adding a custom theme to the current Mastodon theme selector isn't *too* much of a coding effort: https://github.com/ronilaukkarinen/mastodon-bird-ui?tab=readme-ov-file#make-mastodon-bird-ui-as-optional-by-integrating-it-as-site-theme-in-settings-for-all-users
Bird UI and Tangerine UI are the two well-maintained Mastodon themes I know of, although I assume they're mostly (all?) just CSS without touching any templates. Letting server admins install themes of this kind by drag & dropping a zip file could be a nice dev target.