I have cronical hate against Microsoft products due to my software and web development past with them. Even though Metro is nice, I would not consider buying anything having Microsoft label on them anymore. But if it run Android I would buy it: Nokia still makes the best long lasting hardware and interesting form factors.
Sailfish, Ubuntu Touch, Mer, Tizen, Firefox OS, or even Cyanogenmod, if nokia opens up specs or give tools to port other OSs to it probably a lot will. But is not just drivers to port the OS there what is needed, probably the camera program have enough intelligence to need to be ported too to worth it.
Possibly yes, i would need to look in to it more.
however i have not looked in to the camera aspect of the device so i can not agree with the "it has the best camera" part of the statement.
If it had Android, I wouldn't consider buying it.
Yes! No doubt about it (with Android 4.3).
With or without Android, 1020 will fill a niche with professionals who need to take pictures and videos, but are not professional photographers. If you need to carry camera with you always, compact pocket camera is not as good in always part as Lumia will be and quality difference is small. Compact cameras are out. It will be just camera phones and SLR's.