The use of an adjustable suspension hammock would be a good idea to keep the weight of the lens from causing damage to the camera body and/or lens attachment over time. Also it be killer to have the ability to attach a small light weight tripod. This is very much like the Case Logic SLR Sling (SLRC-205) only looks better made and is designed for biking comfort. Add those two features and maybe the option to put a cell holster on the front like a chrome bag and you've made the worlds best (first?) SLR messenger bag.
Wow cool. That's pretty sick. Any other examples or different angles? Wait I found your flickr...