"It's an expensive effort, and the ability to fund an effort like that can be inversely proportional to the willingness to take on the risks you mention." I'd

"It's an expensive effort, and the ability to fund an effort like that can be inversely proportional to the willingness to take on the risks you mention." I'd say you're right and replicating Windows now would be hellishly expensive but it wouldn't have been so some decades back. After all, ReactOS has essentially proved it's possible. Despite the fact that it's not practicability usable it sort of works in limited circumstances (I periodically test it). Given that it's a smalltime backyard effort but can run MS Office on some hardware demonstrates to me that if serious effort were put into its development it would do most of my needs. The other problem of there not being any other API-compatible OS in competition with Windows is that Microsoft has never fixed the many problematic issues with Windows—as it simply never had to. It's too complex to discuss them here but if MS had had fair competition from another OS then end users would have had a much better run.