So on the menu, the tab was always called "Companions" instead of just "Companion" so I was always led to believe that we would eventually get other types of battle companions.

Retainers: Duh! People have proposed this one before so I am going to skip right over it. I would think they would have the most customization options.

Additional chocobos: Probably from breeding, whenever that gets introduced. They\\'d function similarly to the chocobos we already have, but since we breed them they might have more customizable stats than GC chocobos.

Beast tribe allies: This is my main new idea! If/when they ever increase the cap for beast tribe quest ranks, I think battle companions would be cool to buy at the highest ranks. How cool would it be to have an Amal\\'jaa attacker, or a Sylph healer, or any other beastman fighting at your side? We could probably even give them names and such and it\\'d be cool if there were sidequests involving them as actual characters we could do too