well, even if the possible won't perf, the eggs still counted as eggs will almost completely only be back-up dancers, and since the performers aren't listed as "Hello Project Eggs" and only as "Ongaku Gatas" you can safely assume that they will only be there as Ongaku or back-up dancers, also the image of Elder Club, is the older group of H!P, so if the eggs perform songs, it'll prolly be in Wonderful Hearts, the younger division
the only reason the eggs are in Elder Club, is cause Yossie, and Satoda are elder club, and Rika was moved into Elder Club with Viyuden, so to keep it so that groups are only in 1 place, they moved all of Ongaku there
but hey, i'm not Tsunku, and the tracklist for the concert ain't out yet, so I could still be wrong