Then get a Sony if it is such a God send to us humans and get an adapter to use your shed load of Canon lenses.Personally I would far rather see an equivalent of the Sony 200-600mm internal zoom. I've already got the excellent 100-400mm f4.5-5.6 L IS II, and I suspect most Canon users who need this type of lens have. Whereas Canon hasn't got anything like this new Sony 200-600mm. This lens and the Sony A7r mkIV, where you can use it in 26mp crop mode, is making me seriously wonder about the Sony system. For any nature photographer who wanders around in the field, this sort of combo is near perfect. It's not just the focal length range, but the fixed length and internal zoom, which makes zooming in with a flying bird so much easier. If you read reviews by Sony wildlife shooters, most them that have their 100-400mm lens are saying that the 200-600mm in practical terms is much better because of the extra range and internal zoom.
I think Canon needs to learn by just how well this Sony lens is being received by nature photographers. It would be much easier to stick with Canon because I have a shed load of macro lenses, flashes etc. I also think Canon needs to learn from the example that it is possible to have an all round camera that is high resolution, but can shoot fast, have high speed AF and be used as a crop camera.
I love the telescoping zoom as when packing it for travel it is so compact.
12 5/8" vs 7 5/8" is 5" or a wide angle lens and the 100-400. Also for those who do not live doing birds but have large and diverse interests the unique to Canon only of the close focus capability of the 100-400 MII is absolutely amazing.
Perhaps canon will make a longer 200-600mm type lens. And if they do good for them, but for a broader base of users for the RF system the 70-400mm will be exciting. And those bodies, I imagine if the 1DX MIII and the upcoming RS? is an indicator, there will be some mind blowing QUALITY cameras by Canon that are well built and do not act like toys.