Was speaking with a GM about a different matter, and was able to also ask about drop rates and 4.0.3/4.0.3A and I believe I have finally found some form of a response that is credible! Any attempts to acquire this answer from multiple other users hasn't retained much other than it will occur soon(tm).
To the GM's knowledge, the mount changes will not occur until 4.0.3A when the Shattering occurs. Everyone rejoice!