I don't really see the point. Spdy is already supported by major browsers more than this would ever have. Why have half the features when you can have them all? Also browsers would need new APIs to deal with getting the data from slicing as it doesn't seem to properly support something like web sockets (no multiplexing of the input, does spdy support web sockets?)
True, it doesn't help with web sockets but I think it could work very nicely with "Server-sent events"[1]. I believe that in almost all cases (Except gaming) where people are trying to use web sockets you can achieve the same result with SSE.
