Add behaviour achievement mounts
Most of the mounts are used by half the server so at this point you kinda ignore them when you see them... nothing special about them unless in the first month after they are added to the game.
Some of the mounts can only be earned in the harder content, stress that some of us are unable to carry due to our RL stress levels...
We all want to show off sometimes, most through glam but I think the same should apply for mounts. I realise SE can't change the system and allow you to customize all the mounts. What they CAN do however is add more.
Therefor I suggest SE adds "hidden" achievements tied to a mount in which case the mount will "hint" at how you might have earned it without actually showing the achievement or its requirements. You will simply have it sent in your moogle mailbox.
For example you could get a kangaroo mount because you jumped around a certain amount of times, or a parachute mount because you often take fall damage, or a mount for using your retainers or the market often, a mount for giving away a certain amount of money, because you healed a certain amount of hp, dealth a certain amount of dps in total, tanked a certain amount, etc... everything could have a hidden unknown requirement hiding up to 100 mounts from people they could potentially show off with and not much people would be able to tell others how they got it meaning it would remain rare.
Lets say that some weirdo goes through the extreme length of counting & documenting everything, putting the info online... sure more people would then end up having it but there are some requirements not easily filled in... especially if you hate the requirements on them (like having to heal when you hate healing).
Lets say that in worst case scenario people figure out all the requirements together...
SE could adjust its tactics by making it temp requirements where they have to meet those hidden requirements within the mount (but a much smaller amount) so only the people who do what they happen to love doing would get it.
And if that mount is made in a way where it relates to the behaviour... it will help others become even more expressive :)
Just thinking out loud, think I fried my brain before I even started this one so I hope you see potential in it.