I'm a firm believer that a "vote as payment" system could be huge and work wonderfully. Months ago I remember a developer creating a tool/site which calculated your top supporters based on how much payout their votes had given to your posts. I've been unable to find it recently, but that kind of functionality to track vote value will be at the base of a payment system.
I envision people running 30 or 60 day KickStarter type campaigns, posting regular updates, thereby giving backers multiple voting opportunities. The software would keep track of the value individual backers have brought to the project, determining their rewards level like in a KickStarter campaign now. The same system could be used in an ongoing Patreon type manner as well, or for one off product ordering.
This would drive demand to hold Steem Power. Growing or investing in your account would allow users to effectively participate in these types of activities. It could pretty much be the worlds largest loyalty rewards program!
There is an old gambling saying which states "Whoever invented gambling was smart, whoever invented chips was a genius." Chips divorce the gambler from the concept that they're actually betting real money. Likewise, voting is Steemit's version of chips. It is much more frictionless and mentally easier than making micro payments that actually deduct from your Steem balance.