Well to put things in perspective, a class and a race don't really overshadow each other. In fact, the model upgrades would be a great feature alongside a new class. However, model upgrades and 2 new races would be an issue, because the 2 new races would overshadow the model updates.
As for class updates, in MoP, both Druids and Warlocks got class overhauls, and the Monk class came out just fine. So I don't see the Hunter and Rogue updates as a major obstacle, especially since Blizzard said it wouldn't be a complete change like Warlocks.