It is pretty much impossible to build a lens with that wide of an aperture that is also so long. As mentioned, at 200mm the lens opening is 166mm at f1.2. This would be a physically immense lens, even more so a fi it's a zoom.
If we restrict ourselves to an aperture that's realistic (say f2.8), the only issue is that such a lens will need to be very, very big and expensive. These lenses exists, and are mostly bought by broadcasting companies for covering sports.
An example is the Fujinon 25-300mm f2.8, which weighs 10kg (23 lbs) and will cost you $44,000.
Or even more extreme why not a 9-900mm f1.7-4.7, for a cool $100,000. These lenses are however NOT sharp. They are made for video, which is why they can have such a large range, the latter lens for example only resolves 2MP.
If you also want the sharpness of say, a Canon 200mm f2 prime on your zoom lens, it would need to be even larger. The Sigma 200-500mm f2.8 is an example of a lens made for still photography with both zoom & large aperture. Note that it needs to be even larger than the Fujinon while having a much smaller range of zoom to retain acceptable sharpness for stills.
You can read more about the 25-300 at lensrentals.