It's was confirmed on Twitter that the guys - at least Joey and Donnie for sure - were back in the studio yesterday working with producer RedOne. I'm not sure if this is for the NKOTBSB album or something else...
Here are some quotes from Twitter:
Joey: Question: I'm in the studio listening to Donnie sing the Right Stuff in the vocal booth next door. What year is it?
Donnie: How come I'm singing the Right Stuff in this booth here but Joe is singing some new RedOne heat in the next booth over?
Donnie: All done in the lab! Thanks to my dear brother @RedOne_Official Another amazing adventure together!!
RedOne: Yes i am with with my friends, @NKOTB as we speak :-)