That same youtube channel is now predicting a 300-600mm with a constant 5.6 aperture. that makes more sense but honestly, its been too many years and too many false rumors to believe anything before canon actually announces some hint officially. Constant 5.6 makes sense since it would be an internal zoom most likely, and 5.6 is faster than other companies 600mm zooms are, so it will look good on paper in comparison. Although practically speaking 5.6 and 6.3 are almost equal.