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.
As you can see from this screenshot we took on the European PTR, you'll need exalted to buy a mount (as you do currently), but the items have become bind-on-pickup. We can't tell just by playing on the PTR exactly what will happen to our existing riding skills and mounts, so here's hoping we find out more about this change soon.