It might be nice to show a quick intro message for first-time user, could be implemented via GuidedTour. We may want to distinguish between new vs. experienced users.
Part of the goal of the message would be to help users understand the difference between editing in wikitext and VisualEditor, and to explain that wikitext cannot be entered in VisualEditor. We're seeing a fair number of users enter wikitext in VisualEditor, and adding a first-time explanation might help reduce this issue as we roll out VisualEditor to more wikis.
(Feel free to close this WONTFIX if we decide this issue is not significant in scale enough or the message would be too prominent. But having a first-time use message come up is not that unusual for a major feature change.)
T51820: VisualEditor: When user types in '[[' in the page or another DOM input widget, pop up a reminder that they're using VisualEditor
T89074: Offer new users of VisualEditor a short guided tour