Updating the lens after 5 years? That would be quick. Is having a superior 800mm lens that important to Canon?
Well, you could look at it that way.
Or you could be excited by the fact that this quick replacement means that Canon has yet again exceeded its own high bar. The original 800mm was sharper than the 600mm IS + 1.4x. Now that the 600mm IS II + 1.4x is sharper than the 800mm, not to mention lighter and has better IS. Currently there is absolutely no reason to buy the 800mm, since better IQ and greater versatility can be had with the 600mm and 1.4x III (for almost identical prices). Canon knows this and will update the 800mm accordingly.
I know only a very small minority will ever own or use this lenses, but it certainly shows Canon is able to surpass itself in a very short amount of time, and that should make all of us happy (except for the climbing retail prices on these new items).