It was upgraded a few years ago from the 35-350mm L non IS. Don't look for another upgrade soon, its a very slow seller. The lens was used by photojournalists, but they seem to be fewer every year, so the main customer base is going away.
I've had both the 35-350 and the 28-350, and they are excellent lenses. A 10-1 or 11-1 zoom is a big compromise, so don't expect the same IQ as a 3-1 zoom, it won't happen. This is by far the best of the super zooms.