From reading the articles, it seems NHK wants to improve the Kouhaku ratings this year by drawing in the otaku crowd with AKB48, Shokotan and Leah Dizon performances. They'll be in a special segment (I think they'll be the opening performances? I'm not sure).
I'm looking forward to seeing AKB48 and Shokotan. I just hope that this won't endanger the chance for MoMusu to appear at this year's Kouhaku (after all, the NHK people might not see the point in having two girl groups with large amounts of members performing).