I don't see the point in using a Bitcoin-esque protocol for a voting system (ie a hashing based blockchain). In fact the existence of a double spent vote could

I don't see the point in using a Bitcoin-esque protocol for a voting system (ie a hashing based blockchain). In fact the existence of a double spent vote could simply invalidate both (or all) votes; the user attempted to cheat, no need to decide which is valid. Otherwise vote acceptance could be based on the votes of the ids themselves rather than by hashing power. You say decentralization is a key aspect, but the distribution of whatever underlying identity the users are voting with still has to be centralized. Bitcoin has opened people up to these sorts of ideas, but that doesn't mean it has to form the basis for everything in the future.