If you could add 1 item to the mog station.

[Felis]

Those will forever stay 1.0 legacy. No way SE will ever touch them, they'll set most of us in a rage against them.

But none of them is a legacy item
First one is the "that character got created during 1.0" tattoo, the second a reward for finishing the 7th umbral era story and the mount for talking with the wandering minstrel before the yellow jackets have put him into jail.
But yes, they will be exclusive forever.

The item they can put in:
a 10 fantasia bundle