What happens to Deformer Mesh Clothes now? I was curious about that, so I asked Oz. Nothing happens to them. They will remain in your inventory and you can still wear them. But, they are not going to deform as intended. They will behave just as any rigged mesh clothing does. They will still move with the avatar. But, they will not follow your size changes. Like standard size clothes they will be a single unchanging size.
The asset servers saved these Deformer targeted items with special information in the asset’s header. Only the Deformer Project Viewers would act on that header information and use the Deformer code. Normal versions of viewers ignored the information and treated the mesh as if it were just another rigged mesh attachment.