Well… the r3-s are not really mandatory for leveling Legion professions. But they have actually been unavailabe even from RBG wins since 8.0. I think it was also mentioned in the Collectors Wish List for Professions thread.
The closest thing I can think of is BfA pattern ranks being purchased with badges of honor, but at least those can be obtained via the class order hall mission table (albeit very, very slowly).
Oh, this is a very good question, I hope we get an answer!