Bump and thoughts:

Adding mini-games, especially card games, to FFXIV would be a fantastic idea. Aside from development time there are no drawbacks to adding such systems. Adding mini-games and the like is another distraction for players, just something else for them to do in FFXIV which is never a bad thing.

Card games especially have hundreds of hours of gameplay value if done right. Between collecting the cards, building decks, perfecting decks and of course playing with others casually or in tournaments there is a ridiculous amount of gameplay value here. Buying cards could be a gilsink, collecting cards through other means like defeating monsters, completing quests or participating in events gives players something to do. Again outside of the actual development time there are no drawbacks to adding such a game.