that was the case in mk9 as well... I don't think it will be the same in MKX, those skins seem pretty polished and distinguished to be exclusive to a single mode/kombat kode/test your luck modifier.
I could be wrong, but, judging everything we've been shown so far, I'm beginning to suspect that NRS might give us three on-disc standard skins for each character: Default and 2 Alts.