Maybe I'm a Lion and the Battle with Gilgamesh (Clash on the Big Bridge) have already been done. I don't think Challenge from FFX will get an arrangement. The Black Mages seem to use only songs composed by Nobuo Uematsu, and Challenge was by Masashi Hamauzu. Jenova has two versions by the Black Mages: one in BM1 Album, the other one in FFVII AC OST. They sound like the same, but they're actually different versions.