Yes, B now grants “free” economy plus (so a non-Premier traveller on a Polaris or PremiumPlus ticket with domestic segments in B gets to choose E+ seats.)

Google Flights also shows these now as “extra legroom” fares, roughly similar to Delta’s Comfort+ fares.

The question remains of how, exactly, Premiers are supposed to purchase Y/B/M fares now. (These fares require inventory in both B and another inventory like K, much like the P fares we are all accustomed to now.)