Yeah primarily Maya (but also max for ripping models). There is a modders' pack with a walkthrough that was shared to some people over IRC, but I am not allowed to share it yet.
Right now I'm planning on dividing the mounts into 5 categories in 3 tiers (wargs and horses are considered tier 0);
Tier 1; skath and bears. Skath will be found in swamps, and provide the rider with +1 strength and +1 combatspeed. Bears will be found in forests, and provide the rider with +1 agility and +1 combat speed.
Tier2: Brutes and primal bears. Brutes are found in deserts, and provide the rider with +2 strength, +1 combat speed and a unique charge ability doing +30% damage once per combat. Primal bears are found in hills, and provide the rider with +2 agility and +1 combat speed and a unique ability that increases defense by 100% but removes all combat speed for 1 turn (usable once per combat).
Tier3: Drakes. Drakes will only be found in minor faction cities, they will also only be available for purchase there. All drakes add +2strength and +2agility, and 1 combat speed. White drakes also add a powerful health regeneration to the rider. Black drakes grow increasingly furious as a tactical combat progresses, and will give the rider +3attack and -2defense for every turn that passes. Red drakes add a significant amount of health to the rider.
edit: mounts will also give health bonuses according to their tier, so tier1 adds 1 health to units riding it, tier 2 adds 2 health and tier 3 adds 3 health. edit2: this will be significantly higher for champions.
There will also be armoured horses and wargs, which will be brought in from the barded horses mod + a barded warg model, and they will be equivalent to tier 1 mounts, but will cost a lot more than just the "mount" resource (ie, more than just a warg or a horse). All the other mounts will be free of charge if you have the "mount" resource for units.
Of course this will be adapted to suit the new mounts in 1.1.
edit: also, umberdroth will be somewhere in there, probably tier 2.