Implementation of chocobo can really open a variety of "new" gameplay elements to the game. I think the use of it should be limited fo the first levels, until 15-20. Some ideas,

- you can rent it from lv 10 to 20, for a (very) limited amount of time. A normal one, without abilites or stuff (you could be attacked and dismounted from particular mosters, like the flying ones).

- from lv 20, you can rise a baby-choco (egg obtained by a special chain-quest). Or buy an adult one. You can give it a name (not from a list pls! ). You can call it in every moment with a whistle item.

- your chocobo will have levels (baby= 1-5; young=5-20; adult=20-max). Every levels it can increase HP and other stats (customizable allotment). At different levels, it can acquire new abilities/traits. At a certain level, it can partecipate to the war at the front (PvE Companies content.. campaign against Garlean?).

- you can customize it in every aspect: equip, abilities, color, etc.:

* color = this can be done during the baby-choco period of raising (with particular food or 'training').

* equip = you can equip your choco:
armours (to fight on mount and to have a greater chance to not be dismounted by a mob attack);
bags (to add more inventory space, usable with choco presence only);

* abilities = your choco can acquire (by training) or buy (from special vendor, with some sort of tokens) some abilities/traits, like:
jump (to reach high places..maybe it could have 1-3 levels of jump);
dig (to search for items and gil);
war-choco (it can attacks enemies.. in that case it can be equipped with iron-beak parts and stuff);
charge (it can charge an enemy causing more damage, only if in a right distance);
sprint (increases speed for 30 sec or so.. 1-3 levels also here);
messanger (you can send items to another player mailbox or house if any, depend on chocobo bag space. In that short period -15mins?- your chocobo will be unavailable).


And so on. Btw, there are so MANY possibilities that it could be a game in the game (like housing eheh).