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.
Oz says the Lindens think it is more trouble than it is worth to figure out how to remove all this defunct mesh from the grid. So, these things will likely remain in your inventory until you remove them.
With both Fitted and Defomer targeted clothes a standard viewer will treat them the same. No sizing change/adaption will be seen. The viewers do not have the code to change the clothes intended to use the Deformer to fit a shape. They will behave as if they were a standard sized mesh item. Only the Fitted Mesh Project Viewer will correctly render the items made for Fitted Mesh with size adaption to your shape.
Some experimental viewers have the Deformer code. AFAIK, those viewers are not being blocked from the grid. They have the old style Deformer code. You could still upload and render clothes made for the Deformer. But, expect that code to disappear as viewers switch over to Fitted Mesh.
Those experimental viewers will not render Fitted Mesh Clothes. Nor can they upload it to SL.
This means Deformer Mesh Clothes and viewers are basically useless. Today I started deleting my Deformer demos and test clothes from my inventory.
The Lindens are still looking for feedback on Fitted Mesh. As long as this change window remains open SL users can recommend changes and have a good chance of seeing them quickly implemented.
So, get the Project Viewer and try them out. Make your recommendation in JIRA FITMESH.