When WikiEditor loads, it takes it about a second to load its toolbar. Waiting for this is an unpleasant experience.
It would be nice if WikiEditor created itstoolbar HTML codes on the server and included them into the page at the time into it is loading.
People wishing to customize the toolbar (https://www.mediawiki.org/wiki/Extension:WikiEditor/Toolbar_customization) would need to be provided an opportunity to specify their button layout on a wiki page in the mediawiki and in the user namespaces, so that these buttons can be included into the toolbar HTML. The respective callback functions could be defined in the custom files on-wiki.