There's an error message that says "This wiki is in read-only mode". During Ops' planned outages due to the codfw migration, is it possible to make that error message say "This wiki is temporarily in read-only mode. Please try again later"?
So we can change ApiVisualEditor->isWriteMode to return false (ApiVisualEditorEdit->isWriteMode still returns true), and add a notice like the one shown on the wikitext editor.
You may wish to copy and paste your text into a text file and save it for later.
Don't think this part of the message is appropriate for VE though, @Glaisher