Lost libraries? very lost. I rarely find them. Lost horses, I only find them playing an empire (and can't use them). Lost wargs - see entry on lost horses. ^^ agree with all the above. I think the idea of allowing BOTH empires and Kingdoms to utilize both horse and warg tiles in some manner has great merit.
I think the intention of the designers was to use the horse warg division to enhance the Kingdom/empire divide, then the current arrangement does that in a very limited manner. its still merely (mostly) cosmetic. Allow both sides to 'domesticate' them both, when the sov has researched it. In short, remove the kingdom / empire restrictions for both horses and wargs.
Now, make horses and wargs VERY different, not just in appearance, but in actual play. May I suggest the following:
Wargs much larger that horses: think elephant. (Yes, I know, wargs are based on MANY fantasy games where they are a kind of wolf on steroids.) But, hey, Elemental is not your father's fantasy game. Its OURs, and its different.
Wargs are larger than horses. A domesticated horse, trained to work with a soldier, can be controlled by ONE soldier. Wargs, however, need a group of three soldiers to train and create the mounted warg unit. Wargs are way bigger, higher melee, greater HPs, etc. but each warg requires 3 men, err... humans err.... sentients to handle one warg. A warg unit, trained, is actually one warg, and three ... sentients.
other trade-off: Give wargs the 'feature' that, even after domesticated, and when mounted, and in combat, one (or more) may freak out, go bazerk, and just attack anyone ('friend or foe' thats nearby. Lets say that every turn there is a possibility that the riders reassert control. But the possibility exists that all three riders are killed and the now 'lonely' warg just gallops for home (original warg tile).
Riding a warg gives you a height advantage. And one of those 'eye' icons so the unit can sight further.