I was originally against the idea (well, to be fair, I don't think anyone had much time to fully think about the idea. It was proposed and on track to be implemented so quickly that I think the backlash against not knowing what the outcome would be, was what shot it down in the first place.)
I still think there needs to be a better way, fundamentally. Right now, regardless of implementing that design or not, it costs opportunity to fight abuse, and it leads to a tragedy of the commons (being more short term beneficial to upvote oneself rather than downvote abuse, or if that design is implemented, being more short term beneficial to keep your SP rather than lose it to cancel someone else).
The biggest problem with that design is that it assumes the targeted account only ever acts in bad faith -- you nullify ALL their actions even if some might be "good".
Sadly, I don't know a better solution. The only one I can think of to remove the opportunity cost is having separate voting power pools for upvotes and downvotes, so it doesn't "cost" to downvote (since you have, e.g., 10 downvotes and 10 upvotes per day to use).