I was surprised that GC actually replied to me on twitter just now so I thought I'd update you guys on why their aren't any cool procs on siege weapons in 5.4.
@Ghostcrawler We wanted the heirlooms to be very competitive, which would be tough if there were procs competing with them.@Ghostcrawler Procs are cool. We will do them again. The SoO trinkets are pretty cool in the meantime.