I think it's good that Threads and Waves are viewed separately to posts. I make use of them as I would Twitter with no expectation of rewards.
I can imagine a scenario where hundreds of people sign up and vote for each others 'low quality' posts. Downvoting them all may be hard, but if we give our votes to the good stuff then that gets more of the rewards. As I said, it will be challenging.
If the price of $HIVE goes up then it will be harder to buy a decent stake and if there are many more users then the rewards will be spread thinner. We have an advantage by getting in early.