This is one OS I've kept my eye on forever, though it feels as though Microsoft will go open source before ReactOS can catch up if anything. I wouldn't mind if certain parts of Windows were open sourced, or replaced by open sourced alternatives at least, not all of Windows. We saw this happen to the Open Live Writer.
Windows is complex enough that I think so. I am thinking of breaking up Microsoft's OS division into a non-profit foundation, funded by hardware vendors like Dell and Intel with no per system licensing fees required anymore for example.
But that didn't happen and Microsoft got a slap on the wrist instead.
Many people migrated to GNU/Linux or Mac because Microsoft had abused their monopoly, some people and companies are stuck with Microsoft because their business needs Windows to run their custom apps.