Earlier quoted context omitted.
>I think virtual machines are the best way to keep old software around. You're not wrong. However I think that the appeal of ReactOS (in part, and if it was more stable) is that it's currently updated and (in theory) can be secured against modern threats; so you'd be able to put it on a network -which would be masochistic to do with Server 2003 at this point. I could also be modified to run modern Firefox, chrome, et…
Your post seems to assume networking with internet connection is required by the user. Not necessarily the case. If a company buys a red team test, a Windows XP machine without networking has a different threat model than one with. Also, Wine on Linux might be better option if its just one incompatible application (with or without networking). In short I would say both (or rather, all three) have their place.
I agree with you, and I think that using WINE on Linux probably gives you more options than using ReactOS.
But in terms of what is appealing about Reactos is that (in theory) you'd have the option of modifying it, and it being (again -in theory) compatible with 2k3 server so that putting it on a networked vm could be an option.
I can't think of a use case for it, and I'm not sure that there's a compelling amount of ~17 year old hardware needing drivers -but it still has it's appeal (IMO).
But by and large you are right -most of the time it's better to either use a supported windows version or to use WINE on Linux.