Mounts that have various speeds, skills, traits and function. Typically with the harder to obtain variety outshining the easily obtainable ones.

I'm personally a huge fan of mount systems that include this kind of variety (GW2, Archeage, BDO come to mind..), but I feel like it wouldn't fly here. We already have people who complain about certain mounts being locked behind difficult and/or tedious content. Now imagine if the differences between mounts wasn't just superficial.