I think we can safely say this has been quietly abandoned, as nothing has been mentioned since before launch, and it's pretty easy to see why they've dropped it (the reasons Sove92 mentioned, no doubt SE quickly realized such a system would be monopolized by players to the point it would just be same handful of FCs locking it to themselves week in week out. That kind of nonsense ruined FFXI, and Yoshi wisely decided to forestall any possibility of it happening again here.
Not to mention it doesn't even make sense with the game's lore (Primals are bad period and we're the 'Warriors of Light' who destroy Primals not summon them no matter what. So yeah, you may as well give up waiting for this as it's almost definitely not going to happen I'm sorry to say.
I'm pretty sure this was an idea that was only recently discussed and was stated for 3.1 or sometime thereafter so just have patience.
I admit I'd love to see this too, but I guess I'm also realistic in that I understand just how expensive such an area would cost in terms of development time needed to add (all that writing for starters). To be really honest, I'd be more happy to have a vieawable bestiary/lore log in the interface, but whatever is easiest to add I guess.
They're probably concerned about how best to ensure add-ons won't ruin gameplay or imbalance the game (I mean, look at the nonsense we're already seeing with parsers). Hacking concerns are probably also a big fact too into why SE haven't said anything more on the subject lately as well. To be really honest though, I'd at the very least just like to see more deeper GUI customization added, especially the ability to change the interface's art style and font (i.e. to 1.0's style, but retaining ARR's functionality).
Apparently this is planned to be added with future rank increases in your Grand Company where you will be able to lead a unit of GC soldiers into a dungeon or raid, so therefore this is most likely still on the drawing board. So don't give up hope!![]()