Sorry, but giving the tattoo to newer players does not allow them to see what we saw, or experience the falling of Dalamud, no amount of youtube videos or lore bits will equal the in-game experience, this isn't a knock against anyone it just is what it is.
Also the game cannot create repeat quests etc because those assets and the world design are no longer in use (hence the entire point of it to begin with).
Adding a new means to obtain the legacy mark for players who were not there for the battle of Carteneau (or logged in during that period) however would essentially cheapen what the mark is intended to stand for, it's symbol both by in-game lore standards and by RL ones of players who were around at one of the most important parts of the game's history.
This isn't like seasonal events which are recurring each year and should always have the opportunity for players to obtain their items, this was for the closing down and subsequent rebirth of the entire game.
I'm sorry that it doesn't mesh with your RP or that you weren't there for it, and I'm sorry that there are players that would use it as a means to lord it over others, but there really is no reason why they should give this out for players that were not around when the event took place.
This is where someone will inevitably ask "How does it effect you?"
Handing them out now (by any means) would lead myself and many other players to question the integrity of both Yoshida and the development staff for going back on something that was expressed as only being obtainable during a limited time, along with the Dalamud Horn and the White Ravens these were all symbols of an old and now long passed age of the game.
I do however have no issue with players getting body tattoo options in the character creation if they wish, but the legacy mark (aka the Mark of the Twelve) holds significant lore importance to a period of the game.