Yeah, motivation is a challenge. It's not pure altruism, because returning rewards to the pool benefits anyone who's creating content, but I think the ideal balance has many more voters & readers than it does creators. Adding upvotes to drive curation rewards might help with that, but of course, people can do that already. In the past, I have thought of the concept of a layer-2 token that gets distributed based on "correct downvoting"... i.e. downvoting that is validated by other voters. But that makes it into a far more difficult technical challenge.