I did see that but I fail to see how it could be overlaid being a JPEG. I'm thinking of the klutz who's using Paint or something who just wants to slap something and get it out there without thinking.
I feel that a link to the BBC's great safe zone layout PSD would be a good idea, consider it as it is a well made file and explains everything fairly well.
My guides are designed for people to design ontop of it, then remove the jpg, and if you are talking about people using paint, a PSD would be no good, and too difficult to understand for those new to Photoshop.
Yes, I feel your idea is too unweidly to use due to it's nature being it something to design on top of and so could be lost when something to go over a design would be better and the PSD which does that is far too specific to help out those who know no better.
Either too sharp a tool or one which is too blunt, bad analogy I realise but I feel that the PNG that ITV Lover created is most likely the best middle ground in terms of making sure things are safe zone compliant.