The SDM845 stuff looks quite promising for mainline but unfortunately the platform is definitely showing its age (and camera is still completely broken on every device as far as I know...)
Still, it's something!
Still, it's something!
Shift6mq is supposedly close, with OnePlus6(T) its more difficult due to I think the way the sensor is connected.
Currently, the Pixel 3a is the most promising device in terms of Camera Support on a Qualcomm device with mainline kernel from what I can gather.