Split up editor preferences into VE and source parts and show/collapse the right part after user toggles the VE/source switch (checkbox) on the top of the Editor page
If I go to preferences > Editation tab, there are some options. But most of them apply only for source editor. But from their description isn't clear, that they only apply for source editor and not VE. E.g. the setting of columns and lines is to me working only for source editor, but it isn't specified there.
Keep in mind that there can be various number of editors (Wikimedia sites ATM use four in default plus some of those sites have some additional due to installed extensions) so the solution has to be scalable.
Going to https://www.mediawiki.org/wiki/Special:Preferences#mw-prefsection-editing I see exactly three items related to VE, all under the "Editor" section, and all next to each other: "Temporarily disable the visual editor while it is in beta"; the "Editing mode" dropdown; "Enable the visual editor and the new wikitext mode in Structured Discussions".
Boldly declining this ticket.