This is now supported, but we also need to update the UI to make it more apparent.
What do you mean by 'unsupported' in this case? Message part(s) with no filter defined either by default and/or by the user, or something else?
Can you elaborate on what the updated UI should look like? Currently it seems that any parts can be :save'd (I haven't tried pipe).
I mean with no matching filters for that mimetype. The UI should just explain the options you have, like :pipe and :save, perhaps with buttons similar to the tutorial.