We need a super telephoto zoom

I love my Canon EF 4/500L IS. It is a great lens, very sharp even wide open. IS works great and the AF speed of the lens is amazing. But sometimes when I frame a bird or another subject I am a little too close and it would be great to have 450mm. Or sometimes the birds is a little to small for 500mm but when I add a 1.4x extender it is too big in the frame. Of course I can always crop the shot taken with 500mm but then I will always loose some data and pixels. Sometimes you can get around this problem by slightly moving towards the subject or away from it, but that is often not possible (for example when you are in a hide).
What we really need is a telephoto zoom lens. Nikon offers an amazing 4/200-400 VR which is very sharp and immensely popular among Nikon shooters. I don’t understand why Canon still doesn’t offer such a lens.
The problem with 200-400mm is, that for many animals 400mm is just not long enough. Sigma offers a 5.6/300-800. The range of the focal length is perfect for wildlife and birds. The problem is that this lens is very long and heavy (it is also knows as the “Sigmonster”). Also, it does not have image stabilization.
What we need is a Canon or Nikon 4/200-500 with image stabilization and a closest focusing distance of about 2.5m at 500mm (great for small birds and large insects). If that lens would have a bigger weight than the current 4/500 lenses from Canon and Nikon, I am sure it would be a big seller. Almost every nature photographer who could afford it, would probably buy it. And probably also most sport shooters and any other photographer who needs or wants a long lens.
So far, nothing is in sight. Nikon recently announced new versions of their 2.8/400, 4/500 and 4/600 with VR (finally) so I doubt that they will come up with a zoom in the near future. Canon announced a 5.6/800 IS so maybe there is room for a 4/200-500.
Sigma some time ago announced a 2.8/200-500. But that is nonsense as that lens is way too heavy for practical use. I wonder why they built it. If they had offered a 4/200-500 with image stabilization and fast AF, they would have had a real winner.
So for now, all we can do is to wait and see if sometimes in the future Canon or Nikon (or someone else) will offer a 4/200-500. Next time you see a Canon or Nikon representative ask them for such a lens. If enough photographers keep asking them, maybe someday they will wake up.