Most motorcycle gear/clothing companies sell replacement armor for their jackets, usually consisiting of an energy absorbing foam. The piece that covers the spine, hip or shoulders should be a relatively flat piece - this might be perfect for this application. Just cut it to fit. Might not be a bad idea to buy a piece of this and cut it to fit your pocket (between body and gun) if using pocket carry.
Agreed. If a head injury doesn't get you, multiple trauma is usually the next culprit. Injury or even castration sometimes comes during the groin's trip up the "gas tank" (some are merely airboxes these days) and over the instruments and bars. Low slung sportbike windshields are merciless here. Definitely wouldn't want to try IWB at 10-2. Smartcarry claims their product acts as a groin protector, but I don't think I'd want to try it! I have sat on a bike with one on - it's not very comfortable in a forward-leaning position.
Leather is generally regarded as the best at resisting abrasion, although pretty much any riding-specific gear is built to take a slide better than street clothing. Your other mechanism of injury is impact - with parts of your bike, with whatever you hit, sliding into a curb, a tree, guard rails (often amputate arms/legs), barb wire fences, sign posts, culverts, drain pipes, etc. Hence the need for back protectors and all the padding/armor that makes us look like Power Rangers.
The more I think about it, seems like the best place for concealed carry on a bike would be a cargo pocket over the thigh (good muscle mass surrounding strong bone underneath) or a shoulder rig under the jacket (not likely to take a major hit here - if you do you're screwed anyway).