Sigma does in fact sell Foveon sensor based cameras. The latest is the "SD quattro" (APS-C 1.5x crop from 35mm full frame) and "SD quattro H" (slightly larger, about 1.3x crop).

I used an earlier Foveon the "quattro dp2" (APS-C, 45mm focal length equivalent), they have different characteristics from Bayer cameras. They get high marks from landscape photographers where the shooting uses the lowest ISO setting and fast operation is not required.

They have less dynamic range, however given the amount of investment into Bayer tech vs. Sigma's spending on Foveon, that might just be due to more advanced engineering of Bayer and not something inherent in the Foveon design.

The DP Review forum for Sigma cameras: https://www.dpreview.com/forums/1027

Quattro is unfortunately no longer "true Foveon", as they do something akin to 4:1:1 downsampling, making it more Bayer-like, IMO obliterating the main advantage so apparent on Merrill sensors - when I take a picture of a model face on a top-end Nikon, I can see "mushy" areas on the skin all the time when zoomed it, moire on clothes, whereas with Merrill I get unbelievable sharpness (like individual hair); I can't go back to Bayer as it can't be unseen and working with Bayer-like cameras just leaves a deep sense of artistic dissatisfaction. Also, when shooting clouds on Merrill, the dynamic range is way better than any camera I've seen; some call it "cloud camera" for this reason.

This is a hotly debated issue on the Sigma forum I linked to.

The "Merrill" sensors (named in honor of Dick Merrill, an engineer and photographer that did a lot of work on that generation of sensor) are 1:1:1 as you mention - each of the photosites pick up all 3 colors.

The "quattro" sensors have the top, blue-sensitive, layer at the full resolution, with this layer also capturing the luminance of the image (which makes for stunning black and white, even at ISO 3200). The lower 2 layers are at a lower resolution than the blue layer.

I did get very high quality 13x19 inch prints from the quattro ; but have never owned a camera that used the previous Merrill sensor, so I can't give a direct comparison from my own experience.

Does the output from a Bayer pattern bother you like that when you shrink it to 50%? Because "100%" means two very different things between those kinds of sensor.

Yes, I can't get the same quality from downscaling Bayer/pixel binning :( Maybe 100MPx Hasselblad is getting it done though from what I've seen. I guess the averaging interpolation is missing out on some signals picked up by my eyes/brain and once you finally see them on Foveon and can't see them on Bayer, you can't unsee it any longer. Of course, Foveon has its own problems, some might be related to immature manufacturing tech like banding or purple-green patches in shadows, but when paired with top-end optics in Sigma Art lenses, I simply can't avoid feeling unhappy with Bayer sensors. I have a perfect color vision as well, so I can spot issues where most people can't.