it will always be a race. If they coded it in proper so that self votes could not be done at all, it would kill a lot of programs. Still if they coded it to where if you have delegated to an account then that account would be seen as a self vote and would be unable to vote on your account. Of course all this would do is force people to send their steem to an account and not delegate to it.
Doing away with bad actors is never going to happen. It does not matter how much code is written it will never be enough to stop greed. and the hunt for easy money. People can scream, whine and rant all day long about steem block chain being decentralized, and it is. The Block Chain is Decentralized, not the protection of the coin, or the other front ends.
People can put and say what ever they want on the block chain. No one is going to be able to completely hide that information they were so proud to post. The protection of the Coin Steem is not decentralized. The witnesses may be the ones that determine how the reward pool works, but does that mean they own the reward pool?
Criminal activity will never end when there is money involved. Those that have it, will do what ever it takes to get more of it. Those that do not have it will do whatever it takes to get it.
I am not sure when the payout window completely ends, not allowed to vote any more on a post/comment. So lets just say it is on day 6 at 18 hours. Code it so that any vote received in the last 5 hours, day 6 hour 13-18, will be erased from the pay out. This give the so called protectors of the reward pool a 5 hour window or better to catch bad actors and down vote the rewards. Of course if they did this then it just lead to complaints of I just saw the post, I wanted to vote the post cause I liked it, or post about well lets just shorten the time frame then to 6 days 13 hours for voting, and completely miss the point.
I have no solutions, will self voting grumpycat style return? no clue. Can it be done as describe and give a good pay out, no doubt. Will the bad actors be caught and if they are will anything be done? Depends on who they are, how big a rep they have and how much SP they have.