I'm not a coder anymore (believe it or not, I used to) but I think this would need to be done in a fork, which makes it very hard to implement. The reason why I say that, is because if it was to be coded into Steemit.com itself, it would simply be a simulation of such VP going down, and not the real thing, thus it would simply be easier to go into busy.org or any other application that communicates with the blockchain to keep on abusing self voting.
Don't get me wrong, it's not that I dislike the idea, I just think the witnesses would not vote on it, since they can see easily how it can be circumvented, unless, we were talking about forking Steem again...
Hopefully a witness could give you some input regarding this..
Yeah, this is less of a "let's do this right now" idea and more of a "this is something we might want to think about in the future" idea to get people's thoughts going. I think this issue will have to be addressed at some point so I'm hoping that we can get some good ideas in the minds of the witnesses/developers of steem so that maybe in the future they can find a way to implement something like this.