There's no bounty program (or way to financially incentivise particular features at all, really), but since it's an open-source project and accepts third-party

There's no bounty program (or way to financially incentivise particular features at all, really), but since it's an open-source project and accepts third-party patches, you could consider hiring any freelancer to put in the work. Send them to #sr.ht on irc.freenode.net and I'll show them the ropes.