This change was implemented after the latest revision of the patch notes was made available for inclusion into the 1.12.1 patch binary. It will be documented in a future revision however.
There will be effectively two riding skill levels, apprentice and journeyman. The cost for the riding skill will be significantly higher than it previously was, however this is offset by a drastically lower cost for the actual mount.
For current players with mounts there will be a seamless transition to the new system. You will continue to have your mount; you will continue to be able to use it, etc. What this change does for players who don't yet have a mount or an epic mount is take the emphasis off of the mount itself, and put it on the riding skill. This helps give players access to more variety without requiring a large monetary investment if they, for instance, just want to pick a different colored horse.
