A true blackout would be hellish: I don't know that there's a day that goes by that I don't read something on Wikipedia (which is the point, of course).

A simple, but effective, solution would be to simply change the site's style to draw all article text with a black background, a la redacted documents.

If this was done, users could still manually highlight using their browsers to view the text (and screen readers would still work just fine), but the effect would be still be striking, to say the least.