i think in ffxiv, with the way the regions are where u dont zone but just walk in, if your on a chocobo, and u reach the gate, it could give u a pop up window saying that the chocobo does not want to go any further and ask if u want to dismount.

i think an auto dismount will upset a lot of players, especially if u enter the gate by accident.....

i really REALLY hope they implement something like a personal chocobo barn where you can have maybe up to 5 different chocobos that u've raised from an egg. you can pick and choose which one you want to ride also and instead of zoning in from the rental, you can zone out of your barn which can be a zone right outside the city gates.