The easiest thing to solve this issue would be to define your own operation on the blockchain similar to the resteem (which I don't believe is native to the blockchain, but is a custom JSON operation). I would imagine most interfaces would simply ignore these operations.

Also there is Markdown that can be used to hide information from users on these blockchains but still display non-marked information so you could supplement content in that way if you wanted to develop a pseudo-scripting language from Markdown's invisible ink. Although option one is definitely more practical.

As for deriving a new voting mechanism, you are right in that it isn't really going to happen using the current infrastructure. Developers are going to have to be more creative than that. Although, I'm sure you could figure some roundabout way using option one listed above.

Just some thoughts from someone who has played around with the blockchain API.