He didn't say 'an open source Windows 7', he is asserting that wine brings the valuable bits of Windows userspace that he needs, that Windows 7 was plenty and Wine has at *least* caught up to that, as far as he can tell. Essentially that Wine has had 17 years to catch up to Windows 7, and Microsoft hasn't usefully innovated as a platform since then.
That said, it's a mixed bag, some better some worse. Wine actually has developed support for platform features newer than 7 including the big UI toolkit changes and, critically, DirectX 12. Of course they have gaps compared to even Windows 7.
ReactOS as you say is more an XP-alike and *way* behind. The thing is it's trying to be more a true full recreation of a Windows environment, when mostly people would be satisfied with application compatibility on an otherwise different OS, which is where wine shines.
Other than application compatibility, I can't see why anyone would *want* to run Windows. Since 64-bit RISC Windows couldn't run any existing windows applications *anyway*, I just don't see why people would want to.
Besides, once they get into a proper win32 implementation, that's too useful and risky to open source. The only thing giving Windows a tight grip on the market is the ability to confidently run both legacy and new applications.