Tbf the entire reason Keito made a selection process was to dissuade people from joining during the war, but with akatsuki being 'reborn' he probably wouldn't do it. A much stronger case would be the fact that unlike many other units, akatsuki has never entertained the thought of having new members join, even when krk graduated and Souma was thinking of college. They always assumed it would be three people for the rest of the foreseeable future. I actually think it would be interesting to have Ibuki be sort of a physical consequence of their activities in Okinawa. Unlike Ryuseitai, they were more fixated on the competition, and being winners in the region, may have contributed greatly to hurting the local idols.