Add ability to display Gzipped HTML, Patch, PDF, Plain Text files etc. as if they were not Gzipped compressed.
That may be a job for a plugin. (Plugins can alter the rendering of attachments, like the TNEF plugin replacing the MS crap with normal things).
I forgot to list several MIME Types of PDF.
Just FYI, for plain text gzipped files you can use an Action:
gzip -dfc %p |