I suspect not legally possible. There is a lot of code in the NT kernel from various other companies that at least at one point was under NDA, and a lot probably still is.
It was a free download for decades before being open sourced. From what I heard, it increased support contract sales quite a bit, letting companies feel that that weren't necessarily tied to Sun for Solaris, but knowing that Sun was the best outfit to support it.
> I bet no one that downloaded it has spent a dime to Sun.
You would lose that bet hard. They made their money on hardware sales and support contracts.
A family member of mine was the head of Federal Sales for Sun at the time.