I'd rather kill karma entirely than refactor it into an upvote-only system. If you're trying to do anything more controversial than deciding which cat picture is the best, upvote-only systems encourage nasty factional behavior that I don't want to see here: it doesn't matter how many people you piss off as long as you're getting strong positive reactions, so it's in your interests to post divisive content. That in turn leads to cliques and one-upmanship and other unpleasantness. It's a common pattern on social media, for example.

The other failure mode you get from it is lots of content-free feel-good nonsense, but we have strong enough norms against that that I don't think it'd be a problem in the short term.