Great points.
One possible caveat is the limit to the amount of vote power each account has. Voting strength may need to be able to be manually capped by the user or simply vary automatically by Steem account stake (Steem Power).
Yes I suggested have the ability to set some limits to prevent over draining accounts. This would need to fine tuned.
Another caveat is the limitations of the Steem blockchain to posts. You can't upvote a post multiple times, so paying for multiple plays from the same user may be tricky or impossible. There's also the 24 hour + extension then 30 day payout schedule.
Yes perhaps there are some ways around this. For example each play could appear as a new post - obviously this could be problematic from a storage perspective though. I don't think the time issues will be too much of a problem though.