I think a lot of people hope you are reconsidering your plans to do this. It's a nice idea, and your motivation is good. It just won't work in practice. So, in my nicest and most appreciative tone, I would like to ask you on behalf of myself and many people who are also appreciative of your efforts and your motives to reconsider and abandon this plan.
I'd be happy to abandon it if something that accomplishes the same job, or substantially the same job, shows up before it goes online.
Have you considered using NoCeM's to do this? This would be much more opt-in, as somebody would have to specifically configure NoCeM to accept your key. It is also much more efficient than cancels, at least propogation-wise. Just a thought from a news administrator who doesn't want to be processing 300,000+ cancels a day all of a sudden, -------Scott.