Or maybe they didn't want to tell and leave him as a big question mark. This happened before, no? Does NeoExDeath ring a bell? He was even more sudden and unexplained than Necron (still loved him, though).

Either way, he was still an great Final Boss (IMHO) with some awesome music (IMO) and one hell of an annoying attack (Grand Cross).

I think it wouldn't have felt right if they just had let it end with Trance Kuja and it wouldn't feel right either if Kuja transformed again. So I was kinda glad Necron appeared (though I was spoiled, I knew he would appear).