At 1080P, it's not just reading 21% of the sensor, otherwise you'd end up with a very cropped in image. Instead, it's reading the sensor and binning or downsampling to get to that final resolution.
I'd say the chances are slim that this changes in the future.
This is correct, it reads the whole sensor and then throws away data until you're left with 1080P. I don't know how the
Air 2 does it though, there are a few ways to do it - binning, subsampling, or line skipping. The
M2P for example uses subsampling to get 4K from it's 20MP sensor in FOV mode, which is not a good way to go about it.
Sony do produce 1in stacked sensors and use them in their RX100mk4 onwards and the RX10mk2 onwards but they only seem to sell the smaller mobile phone sized sensors like the one in the
Mavic Air 2 using the faster technology. Panasonic and Canon have used 1in sensors from Sony in their own cameras but the BSI versions and the full frame stacked sensors used in the A9 and
A1 they also seem to have kept to themselves.
Sony Semiconductor is a completely different entity than Sony Imaging and for the most part, they will sell any sensor to anyone for the right price and they will also license their technology to others for the right price. It is far more profitable for them to operate that way than keeping the good stuff all to themselves. It is a much larger business than their imaging company and operates separately. They will either sell "off the shelf" sensors or fabricate them to manufacturer specifications (like they do for Nikon). They also will sell exclusive sensors to other companies, such as the 20MP unit in the Nikon D500/D7500. Sony also makes stacked BSI 4/3 sensors and Sony does not sell any 4/3 cameras to put them in - the Panasonic GH6 will likely have one of these units. Sony also sold stacked 1" sensors to Canon for use in the G7XIII and G5X II.
Nikon's Z9 uses a FF stacked sensor that is likely fabricated by Sony even though it is a Nikon design. This still needs to be confirmed but I will be surprised if something has changed there. The other possibility is a company called Tower Semiconductor, which Nikon has a 20-year-old relationship with, and if they are the manufacturer of the Z9's sensor, it will be their first of that type, which is why it's less likely, especially since such advanced sensor production is very difficult to scale. They do however have Xperi licensing, which is the bonding technique everyone uses for stacked sensors. Canon also now has their own FF stacked sensors in the R3, however they are not up to the level of the Sony units with regards to performance, particularly with readout speed or resolution. To my knowledge there are no other companies capable of producing FF stacked sensors at scale - modern fab lines cost well into the billions which is one reason why there are so few players. Panasonic, Toshiba, Renesas, and Aptina all used to make camera sensors in the past but most of their fab lines have since been sold off. Omivision, Samsung, and Sony are all currently making stacked sensors, but the former two only in smaller formats. I am extremely curious to get confirmation on the Z9 sensor, as there are only two possible manufacturers for it.
