I completely agree, except you are preaching to the choir. The preview already includes the text:
[snip]

That's what I meant with "which is not really an excuse for not reading that they're discouraged anyway" in my reply to this comment of yours.

OTOH with "visually distinctive" I meant something that should really catch the eye, e.g. like someone else said, bold red, at least in default themes - if someone changes that, he will be on his own. But then again chances are he/she will already know what he/she is doing. And of course all this wouldn't be in substitution of the current warnings and reminders, but in complement to them: of course one may not want to see such visually "invasive" warnings under normal circumstances.