Pay for your inventory.

[IceWing]

add a junk bag on your chocobo were you place what you consider junk you want to get rid of by sending your chocobo companion to sell off those items to free up slot and returns after a few minutes while still on the field!

This seems entirely useless to me. This isn't XI where you had to walk for hours to get anywhere. If people need to sell junk then there is a merchant in every camp to do so, and camps in every area. Not to mention the ability to just teleport to any town nearly instantly. If they were to remove teleports, and airships then yeah this would be handy but this isn't that sort of game.

Instead as someone said earlier, nearly every item has a use, and every piece of gear appeals to someone. Meaning people who like to have things on hand to craft whatever they need or those who like to change their outfits once or twice a week on each job are punished and required to pay for bag space to hold those items.

However if they were to add some sort of storage chest furniture to your private house, or attached to FC chocobo stables, and the chocobo is able to take items from you and take them directly to a storage chest, or fetch items from that chest if you were to wait a few minutes might be useful purely as another form of storage.