I think I have an idea:
THE STEEMIT UPVOTE CAPTCHA

a bot that verify the human upvote...like a "captcha" type of bot that at the moment of upvoting it will ask you to write down a funny looking word lol...

"self-upvoting" bots would die in agony

also it would make you think twice before upvoting .. thinking about the time you have to lose to "captch" it...

...so you must really like a content to go thru an upvote..

am I missing something here? what do you think...