Cash shop currencies only exist to obscure the actual prices of things. People are more likely to blow money on stuff when they can't easily see how much they're spending. Most cash shops force you to buy the currency in bulk as well so you have to buy more than you actually want to spend.

The fact FFXIV has none of these dirty tactics being used in their cash shop so far is a very very good thing. That someone would ever ask for such a currency to be introduced leaves me scratching my head a bit...