Great idea to take a fresh look at the PFD from the SUP perspective, specifically for the river. Many jackets out there may or may not be the best for stand up paddlers as they where designed for kayakers. We should make sure that anytime we use a piece of equipment we stop and ask our-self the questions "Is this right for me and what I want to do?" I buy things that are designed for kayakers or surfers, or sailors all the time for SUP, but they also suit my needs without glaring compromises. I also still kayak and surf so from a financial stand point it is great to kill 2 birds with the same $100; given your are not opening yourself up to risks that you are unaware of. I very much appreciate Corran and the other designers, manufacturers and innovators posing questions and trying out different solutions.
For me I think it is important for their to be options for paddlers, with respect to all safety equipement especially leashes and PFD's. Helmets should be included in this as well; we should as an industry at least ask the questions. If the answers is something that is already out there then go buy it.
I would say that any PFD that is not USCG (in the US) and UL (Underwriters Laboratories) approved should be approached with caution.