You wrote "downgrade of the 1-inch sensor to a 1/1.3-inch image sensor. The latter will also likely apply to the Vivo X100 Ultra's successor, which will also have a slightly smaller sensor, but will utilize three cameras of roughly the same size."
1/1.3-inch sensor is not slightly smaller than 1-inch sensor. Sensor area of 1-inch sensor is 116 mm2. Sensor area of 1/1.3-inch is 69 mm2. It is 40% percent smaller. I am using Pixel 6a. I am living in Belgium. I am planning to go to Hong Kong this summer to buy some electronics. I want Vivo X200 ultra but if this downgrade will happen, I will never buy definitely.