I'd imagine demand isn't that high for it. It'd have to be absurdly high for them to consider it, where even then, it still isn't all that likely. Diminishing the value behind those limited time goods is probably something they don't want to do, sort of like the legacy Chocobo for 1.0 players. Especially when you consider the general inconvenience involved when dealing with Digital River. A handful of non-invasive rarity in a game where practically everything is otherwise available in some way, isn't really a bad thing. It's unfortunate, but that's usually the nature of collectables.

It's possible though, at least with Cait Sith or the OST minions, that they'd be available at some point on the mog station, given that the means to obtain those involved money to begin with. Side note to anyone questioning the Cait Sith minion on that, given that it was free: pre-ordering and then purchasing the game does involve money.