This thread, and indeed this topic seems downright silly to me. While their aer corporate events that may, in reality may end up with adults only, I think the idea of an intentional no kids day would be a PR disaster for Disney. Don't y'all think the big news media outlets would have a field day with this? Don't ya think folks would get all fired up about it? Just read this thread.
And personally, aside from the above, I think it's a lame idea.
It undermines the whole idea of what WDW is supposed to be - family entertainment. It would undermine their whole message. If you don't understand that, then I don't think you understand what WDW is. It's just that simple.
There are plenty of other vacation destinations that ARE better suited for adults only. If that's what you want, then it's time for you to try a different vacation destination.