So what's the blocker? A good name and label for the new type of vote. Note that the name has to be good enough to not confuse people terribly, even those who are used to the current scheme, and do not see the announcement.

People who don't see announcements eventually have to notice and adapt. I miss announcements all the time.

I think something like

( ) ++     ( ) --     ( ) += 0     ( ) no vote

expresses the intent well, even if it means changing the semantics of "+= 0". I think people would notice and adapt to the new option immediately.