I found reviews of the Sierra Designs Flex Capacitor 40-60L.  It is an interesting light weight pack but it's not really a "snow" pack.  It serves the same purpose as your Osprey Aether AG 70 but will be less convenient to use.  It is basically a compressible single bag which is a simplifying light weight concept requiring greater attention to packing organization.  I don't think it is what you are currently looking for.