Lightning in XIV

[Keyln]

AFAIK the only one who is the exact same character in multiple ff games is Gilgamesh

Well, Cloud has been in Final Fantasy Tactics too, and there's Kingdom Hearts...

But the only character to make multiple appearances is Gilgamesh, and he's appeared in V, VIII, IX, and XII. (I don't count XI, because that's just a character named Gilgamesh, but not THE Gilgamesh).

[Yrusama]

Well, Cloud has been in Final Fantasy Tactics too, and there's Kingdom Hearts...

But the only character to make multiple appearances is Gilgamesh, and he's appeared in V, VIII, IX, and XII. (I don't count XI, because that's just a character named Gilgamesh, but not THE Gilgamesh).

Exactly, Gilgamesh is known as the single most recurring character in the series, even over Mog, and it's because he can travel between realms via the void. Giving Lightning that same capacity would just be annoying.

If they want to have an allusion, even a pretty strong one, I won't object too much. Given Cloud of Darkness, Omnislash, and a Warrior of Light helm, I think it's only fair that XIII be given the same treatment. That being said, I'll be damned if they try to make a canon inclusion of Lightning.