I was just mulling this over, being on a legacy server and seeing so many people with Legacy Tattoo's, myself included and it got me thinking. They should consider adding the Legacy Tattoo to the Mog station.
First off, the legacy tattoo might seem only relevant to those who actually played 1.0 because it's suppose to be a symbol of "being there" during the calamity. Though moving into 2.0 and beyond, the calamity wasn't only a part of the games history, it was a major plot point of the entire story. The calamity was also the entire starting part of binding coil, and the storyline.
Second, someone might say that the mark is suppose to represent being there as they're branded by Bahamut, but to be fair we don't really know what our new characters were doing. They're essentially treated as warriors of the light and as the game progresses the minor differences in the story grow less and less relevant and everyone quickly becomes synonymous with each other.
Additionally, everyone loves extra glamour choices and squeenix probably doesn't want to limit what people can have. They seem to be taking an approach of "Make everything accessible" through the mog shop, which is a fantastic idea. It gives an extra option to support the game, and gives access to rare treats you otherwise couldn't be there for.
Those who were legacy already have other special things, like being in the credits, having the chocobo and gobbue, also cheaper monthly fees. It doesn't seem that bad of an idea to make it another accessible option for vanity.