that a rationally discoverable set of ethics might not be as sensible notion as it sounds.

That wasn't the point I thought I was making. I thought I was making the point that the idea of tractable sets of moral truths had been sidelined rather than sidestepped...that it had been neglected on the basis of a simplification that has not been delivered.

Having said that, I agree that discoverable morality has the potential downside of being inconvenient to, or unfriendly for , humans: the one true morality might be some deep ecology that required a much lower human population, among many other possibilities. That might have been a better argument against discoverable morality ethics than the one actually presented.

But on the other hand human preference satisfaction seems a really bad goal - many human preferences in the world are awful - take a desire for power over others for example. Otherwise human society wouldn't have wars, torture, abuse etc etc.

Most people have a preference for not being the victims of war or torture. Maybe something could be worked up from that.

CEV is the main accepted approach at MIRI :-( I assumed it was one of many

I've seen comments to the effect that to the effect that it has been abandoned. The situation is unclear.