My thoughts before I left the project were to add increased granularity of queue times via having headers added at each passing server and show a rainbow chart for the 'depth' of queue at each layer, not sure if that ever got added.

There's facility for that in the Agent, to allow multiple copies of the header and use whichever came first (for the beginning) and whichever came last (for the end ), it'd be relatively easy to hook metrics into each of those.