Since there is significant controversy on the actual role Visual Editor plays in many wikis, there's discussions on the SingleEditTab feature here and there (see T159032, here, T132806 for a small sample of what's going on) . We need some more specific data. Yet it seems the Editor Engagement Dashboard has been down for quite some time now. Is there a chance to re-open it? Ot at the very least publish some updated statistics? I'm most interested in pl.wikipedia and en.wikipedia, but other wikis might also be interested.
Relevant and permanent resources should also be linked from the main directory https://meta.wikimedia.org/wiki/Statistics