Which classes are getting completely overhauled? Can't really think of any, sure some get significant changes, while for other classes are generally smaller. But i don't see any complete overhauls where most of the core mechanics of a class completely change with how they were before like you usually see in between expansions.
For Raid Tier patches with a quite some class changes check for example most of the tier release patchnotes from vanilla to the end of MoP, this happened nearly every raid tier patch up to WoD atleast and those raids were usually open for progress at the highest difficulty the same night that the patch released.