It sorta makes sense though. A 'battle' scheme like this, as meaningless as it is, will surely boost the sales. Just look at what it did for Nogizaka VS Sasshi last time.
They are really playing into the fans' "who is NMB48's top member" feelings.
I think Milky made the biggest leap ever in Senbatsu Sousenkyo history by coming from an unranked position to #19.
The year before they focused on Sayaka to get at least one NMB48 member in, but now that they are getting bigger as well her position as being the groups #1 isn't guaranteed anymore.
It's cool how each group has like two aces who are supposedly rivals in one way or other. The Acchan VS Yuko thing has been done several times and now we're getting the same for NMB48. SKE48 has W Matsui, but I think their case is somewhat different as they are so different from each other in both age and character. I'm sorta glad they decided to do this battle for NMB and not a Jurina VS Rena PB battle, because I feel Rena's release was a bit more special this way. On the other hand, any PB is better than no PB.
Anyway, looking forward to what the PBs will be like. I like Sayanee's guitar skills, her cool image and ...boobs. Milky's flirty-ness and mix between cute and sexy will surely translate into a great PB as well. Definitely a tough choice and it's very hard to predict who will sell more.