Blizzard are going to release a huge content patch prior to release of the expansion, much like they did with TBC. Remember how the new talent trees were implemented, etc? Well, thankfully, things such as achievements, class talent trees and even the new profession, Inscription, will be released pre-expansion. Source.
So strap on your MC boots, don your AQ40 hat and get those raid achievements while you're still 70. XD
Gaiwyn of Proudmoore