"...selling votes was always going to be an issue..."

Why? because profits nominal to encourage financial manipulation of rewards are potential. The negative consequences to curation, and myriad others, devolve from this vector as long as it remains extant. Tweaks, as we have seen repeatedly, are just playing whack a mole. At this point it's just an excuse to not solve the problem.

The Huey Long algorithm solves the problem, and ends the harm it causes. Vote selling doesn't have to be an issue. It's soluble.