"Would it still be upvote based?"

Executive summary: Yes.

Long, convoluted rant in answer:

Do you only vote because you get curation rewards?

I am willing to bet that most people don't much consider curation rewards when voting on posts. I don't. They're really not financially significant unless you have substantial stake, or you're really intent on your stake for other reasons. Because I just vote for social reasons, my curations rewards are like ~7%, where diligent curators chasing a buck can get ~12% (IIRC. I never tried, so I'm just repeating what I've heard). Almost all platforms that allow comment - all social media - have up and down votes, and only the forks of this platform have curation rewards.

I don't think curation rewards are necessary at all to incentivize people to upvote content they like, because they do it on all other social media platforms without being paid to. They do it for a variety of reasons, just as they like some content, just as they like some platforms, for the subjective reasons that people have to express themselves. Voting is speech too. That curation is honest. People only upvote it because they like it. That's the purpose of curation IRL - but Hive's curation rewards cause people to upvote for money, and this causes the most highly rewarded content to sometimes be crap. Bidbots made that abundantly apparent, and all but destroyed our marketing to anyone but profiteers who thought they might be able to make money buying votes, and joined just for that reason.

Society isn't a business opportunity. It's far more valuable than any business could be. Turning our speech into a prediction market for curation rewards grossly devalues the society that our speech facilitates. Rewarding speech we agree with doesn't do that, but actually helps facilitate society by encouraging authors that aim society in the right direction with their speech.

I think curation rewards being THE means of achieving ROI on Hive is a problem for investors, because they have to spend time finding content to upvote to gain curation rewards or they don't get a return on their investment. That drives them to automate curation, and a lot of people use curation trails for that reason. Curation rewards are most of why manual curation is a bragging point, highly desireable, and this reveals just how badly curation rewards derange the curative function and degrade the quality of speech on Hive. That's the point of bragging about manual curation. It's the same as stating 'I don't derange curation by doing it for money. Everything I upvote I have judged to be quality content.'

Curation rewards are why trending was a seething sack of pus last time I looked at it (which was a long time ago). Trending posts are upvoted primarily because those authors' posts are usually upvoted by whales seeking ROI, so whales seeking ROI upvote them. It doesn't matter if the post is just a picture of a potato, if it gets big votes then it racks up the curation rewards for voters. This is why comments from HBD-funder are amongst the highest rewarded posts on the platform (they certainly are the highest rewarded in aggregate), as you noted (also, HF27 reduced the author rewards for comments, which discourages engagement and makes no sense at all for a social media platform. But that increases the take from curation rewards on comments, and I think it was done specifically because of HBD-funder comments). Trending is Hive's elite marketing department, and that's a shitty way to market Hive IMHO. I mean, HBD-funder one line comments with dozens of 100% votes that will pay out >$100 just screams 'Hive is a scam!' to people we're trying to market Hive to, especially when there's 20 of them posted at a time. And it IS a scam. Author rewards aren't supposed to be funding HBD stabilization, and every pfennig of those upvotes are intended by the original intent of Hive to encourage good authors, to make them happy, so they'll crow about it to the market for our platform, and bring new users here. HBD-funder comments are diverting money from marketing Hive, and there's no good reason for it, because we have the DHF to fund HBD stabilization. The HBD-funder comments deliberately divert that money from it's intended purpose, because the purposes of Timcliff and the curators of HBD-funder comments aren't what's best for Hive. It's what's best for them, and that's not what's best for Hive. If ROI didn't require upvoting something then folks with fat sacks would only upvote things they liked, and they'd be as likely to upvote new, but good, authors as established authors that get autovotes for pics of potatoes.

I think for many investors, a savings account that paid ~20-25% interest per annum would be a godsend compared to curation rewards. Predictable passive returns are why a lot of investors choose blue chip stocks that pay dividends instead of taking higher risks playing the pinks in the hopes of gaining better returns.

Were Hive growing because many good authors were very happy to be posting on Hive, paying 25% interest would be easy to do. If 80% of rewards (all of them except those going to the witnesses and the DHF) less the interest paid on savings accounts, went to authors, subjectively assigned by people that liked their content, we'd have more good authors happy they posted on Hive - and that is our marketing department. Today twice as many rewards go to curation rewards as go to author rewards. That is antimarketing Hive, reducing the happiness authors get from posting their good content on Hive. In every way I can think of curation rewards are bad for Hive.