If people saw that hypothetical page once, I think they might respond to it the way you describe.
But once people subconsciously know what that page looks like, I doubt they'll actually read the text -- they'll just come here, see "oh, news.yc is broken right now" and bounce off somewhere else.
I'm pretty sure this would just subconsciously train me to procrastinate elsewhere. At least when procrastinating on HN there's a chance I'll learn something about programming or business.
I find this idea and noprocrast a tad bizarre. HN has a simple goal (sharing info of interest to hackers), which thanks to focused design it does pretty well. Fixing my brain is feature creep, and should be well outside it's scope.
Fixing your brain is feature creep, but keeping a high signal-to-noise ratio is well within the design goal of HN. If intermittently turning off the site can help accomplish that (not saying it will, just that it might), it seems worth trying.
But once people subconsciously know what that page looks like, I doubt they'll actually read the text -- they'll just come here, see "oh, news.yc is broken right now" and bounce off somewhere else.