Some people say that extremists can do well under PR, but they seem to do well here in the U.S. Tea Party took over the Republican Party, after all. I also think PR is unlikely to happen in our current system.
Yes, I am aware of RCV. I think that that system, similar to Instant-Runoff Voting, is pretty good for races where less seats are up for grabs, such as for an executive position (like mayor or president).