Interesting idea. But, then, I think why not abolish downvotes and just encourage people to reply? Then, you could sort by engagement (i.e. replies and upvotes). The replies could stand in for implied divergence, as there's usually not much reason to continue a long (especially deeper) thread to simply agree.

An exception to that assumption might be if people have unique additional insights that could enrichen a topic, so they're commenting a lot while not necessarily disagreeing. But, such enrichment has notable value in its own right, so is probably worth surfacing as well. Engagement should breed engagement.

>If we want an online space that doesn't become an echo chamber, we need to make it okay to respectfully disagree.

And, that's what it all boils down to. So, the central point is to encourage people to engage and reply with their respectful disagreement vs issue downvotes into a blackbox. The only way to get diverse discourse is to encourage actual discourse. Downvotes are an explicit discouragement of it.