"The fourth factor measures the effect that the allegedly infringing use has had on the copyright owner's ability to exploit his original work. The court not only investigates whether the defendant's specific use of the work has significantly harmed the copyright owner's market, but also whether such uses in general, if widespread, would harm the potential market of the original. The burden of proof here rests on the copyright owner, who must demonstrate the impact of the infringement on commercial use of the work."

It would be up to Microsoft to demonstrate that Wine impact the market for Windows license sales. I strongly doubt they can do that regardless how much they have spent on documentation and developer tools. Wine does not replace the need for an operative system, and if the usage ever become widespread enough to harm the market for windows then developers would just support programs natively for Linux, side stepping the need for wine.

Wine is not a market substitute for Microsoft windows, which is the first consideration that courts look at. Courts would then look if there is a potential existence of a licensing market (ie Microsoft licensing out the ABI) which again does not seems very likely. Failing those two tests it would be a rather uphill battle for Microsoft to demonstrate Wine impact on the market for Windows license sales.