I see, thank you for the clarification! You convert many region attachments into mesh attachments all at once, then you want to use Edit Mesh - Trace on all the mesh attachments with one click.
First, you should not use a mesh attachment if a region attachment can do the job well enough. If your image does not need to bend or be affected by multiple bones, then use a region attachment because it is more efficient (smaller on disk and in memory, less work needed to draw at runtime). In some cases it can make sense to use a mesh to reduce the space it takes in a texture atlas, for example if a large part of the image is blank.
Meshes are used when you want the image to bend or be affected by multiple bones. In that case it is typical to use Edit Mesh - Trace and then adjust the mesh as needed to get the bending to work like you need. The Trace feature outlines the mesh, but it doesn't add vertices or internal edges in the right places so the mesh bends well. It can't, since it doesn't know how you want the mesh to bend (the elbow of an arm, the knee of a leg, a cape, etc). In most cases you need to do additional work after you use Trace. Also there are Trace settings that can improve the results based on the features and detail needed in each unique image.
I agree it could be useful to apply Trace to many mesh attachments at once, but I think it's not quite as useful as it seems at first because in most cases you still need to customize each mesh. It would still save you a couple clicks per mesh, and in some cases you really do want to trace many meshes without further customization (eg to reduce space in the texture atlas).
We will consider adding this feature in the future, I just hope people don't abuse it to make everything a mesh attachment when it would be better as a region attachment.
