played an other game which allowed you to be mounted while in combat. nothing special really except while in combat ie you attacking not being attacked, you slowed to normal walking speed. the mount was only there for the buffs and thus only prized as such. flying was the same way.
it wasn't special nor "KOOL". be careful what you wish for as you will be disappointed more than likely.
Mounted combat was introduced in LOTRO and it was a total mess. So many people hated it because of the choppy, laggy combat. I don't think it can be done well with the current limitations of the engines that MMOs use.