Since voting services get more curation, they can 'subsidize' the vote prices with the curation received. Instead of paying $1.00 for a $1.25 vote, maybe you only pay $0.55 and the after curation margins remain the same.

I did a full analysis for @steembasicincome and this is exactly what will happen. The total rewards going in member pockets from each upvote are not going to change at all from move to 50/50.

Convergent linear and downvote pools are a lot less predictable, depending on your level of pessimism. Largely I think you're correct... vote sellers will find a way to monetize their downvotes. Since demand for paid downvotes will be really low and the downvote mana can't be used for anything else, I expect pricing to be really different than pricing for upvotes.

Is that a good equilibrium? If somebody can buy an 'anonymous' downvote on your content for a fraction of what you pay for an upvote, that's only a good equilibrium if you expect community norms and reputational effects to drive a community consensus toward some normative 'quality'.