Mounts now require only one, shared riding skill (blue mounts require level 75, epic mounts, level 150). Also costs of learning this skill are now significally increased. Previously, cost of learning riding skill was 20 gold for each kind of mount, without any discount. Now it will be 90 gold for level 75 and 900 for level 150. Level 150 of riding skills is required for epic mounts and will most probably include PvP mounts and all mounts that drop in instances (Tiger, Raptor, Baron mount, bug mount and maybe paladin and warlock mount too). For now I can confirm that it is required to ride Stormpike Battle Charger, rest of mounts require confirmation.
In addition to the change of riding skills, the costs of Blue and Epic faction mounts has been significally decreased. Now blue mounts costs 10 gold and epic mounts costs 100 gold.
What this effectively means is that it will be cheaper to purchase multiple epic mounts since the upfront cost of the skill is a one-off instead of the current cost of two epic mounts. This slightly brasses me off personally since I have two epic mounts on my main and working on a third but such is life, it is yet to be confirmed how the change affects those of us with epic mounts already but it is presumed that we will automatically have the required skill.
The important point here though is it is not confirmed whether or not Warlocks and Paladins will require the epic mount skill to ride their 'freebie' mounts. It would be a bit of a kick in the nuts to be truthful since the actual costs involved with both epic quests to obtain the mounts are quite high indeed if you have to pay for all the components, not as much as a normal epic mount but still a long long way from 'free'. It's a given that the PvP mount(s) will require it though so if you want a cheap epic PvP mount get working fast, it only takes a couple of weeks to reach exalted with Stormpike.
It also means that the 'drop' mounts such as the Baron's mount, ZG tiger etc are no longer free at all if you currently don't have an epic mount already. When they drop you'll have to go and shell out 900g to be able to use it.
My point is, it might be wise for any Pala's (I would say Warlocks too but we dont have any high enough) that still need to get their epic mount to maybe do it now in case of a nasty surprise.
