We've seen the patent, and soon we'll see the lens. Tamron is going to join Sigma and Canon with their own 100-400mm lens. The Tamron will be faster than the Sigma at the short end with an f-stop of 4.5 and slower than Canon at the long end at f/6.3. The new lens will obviously be image stabilized and no doubt it'll be priced aggressively.
Now that Tamron and Sigma are both stepping on Canon's 100-400mm toes, it's time Canon get stepping on theirs with a 150-600mm zoom lens. Do you agree?