Last impressive bit of progress in the QM fundamentals I recall was Zurek's einselection, where he claimed to show that only the copies of eigenstates survive decoherence. The approach was unusual enough to be taken seriously, even if the experimental confirmation leaves much to be desired. Carroll's "rational observers must believe in Born rule" looks rather dubious to me, mostly because it still takes a classical observer as a fundamental entity.
The piece that is new is showing that only equal amplitude observers can be thought of as "equivalent" for their definition of equivalent. Previously, one "obvious" thing to try to do was to weight different "worlds" equally, and this answers that objection.
But also important, its actually pretty clear. A lot of quantum foundations papers are rather poor, its nice to see a contribution thats well reasoned.
Edit to add: Just because I think its interesting and clear doesn't mean its correct. In particular, by neglecting t...
Another month, another rationality quotes thread. The rules are: