what you want isn't anything resembling a traditional filesystem. what you want is something like the 'object based storage' things that are being discussed (but you want something far more complex than what has been proposed, let alone implemented or accepted).
defining the redundancy for each file as it is saved will also require changes to every single program out there, which is very unlikely to happen.
if you are willing to deal with different directories having different redundancy options, then what you want is doable today, with no kernel changes. it just needs userspace tools written to make it easier to deal with.