The biggest problem with such a poll is that it won't necessarily reflect the poll that "counts", which is the stake weighted poll that elects witnesses.
I think it's fine to hold such a poll (although I think it can easily be gamed), but I think it would only make sense to do so if a stake weighted pole was also conducted simultaneoulsy. A stake-weighted poll can't be gamed, and it's the poll that really counts, at the end of the day.
Running only a gameable poll that is likely to generate results different from a stake-weighted poll is only likely to lead to dismay when the "poll that counts" yields different results.
I think a stake-weighted poll would work, your idea of doing two comments and the one with the most Steem power behind it wins. Reminds me of how PoW coins figure things out with hash power.
Ok, I'll make up a post after lunch (people are waiting for me now) with the two options. Assuming Steemit is ok with the results, we can let that decide.