As the title says - e.g., the feat Shaping Focus says you need to be a multiclassed druid, would a PrC also count, as you loose wildshape abilities?
I don't see why it wouldn't...
Well a Prestige CLASS is still a different class...
Instead of gaining the abilities granted by the next level in your character's current class, he can instead gain the 1st-level abilities of a new class, adding all of those abilities to his existing ones. This is known as “multiclassing.”
If you are a multiclassed druid, your wild shape ability is calculated as though your druid level were four higher, to a maximum level equal to your character level.
I think the spirit of the rule was intended for base/core classes, but could be used for any levels that don't stack for wildshape. I would default to GM aproval.