Look, no one will ever be as good at being Microsoft as Microsoft is. ReactOS may be eventually be 99 44/100 % Windows compatible. It may look like Windows, feel like Windows, and act like Windows almost all the time--but it won't be Windows.
I mostly agree, with two exceptions. Well, one exception that has an interesting corollary.
There are places where Windows isn't run in order to run Windows, but because there's some kind of "appliance computer" (dental records, machine control, whatever) that needs to run a very specific set of software and nothing else, and that software happens to run under Windows.
This could let vendors who sell those "appliances" stop paying a Microsoft tax, lowering their costs.
The specific case of this that could be of most interest to Slashdot readers: imagine a ReactOS Steambox. Imagine if the Steam client knew about ReactOS, and in cases where a game wasn't compatible, made that clear. (So, you'd get less games than you do via Steam under "real" Windows, but more than you currently get via Steam under MacOS or Linux.)