Xp is an empty station, not a train. In few years most apps and hardware will be incompatible with or not fully functional under xp (they already are in half). I'm not attacking reactos as you could think. I'm pointing to obvious facts that have to be dealt with for success.
If we skip practical part, ReactOS is great as any big community-driven project, because driving a big project is hard.
No (sane) company's migration path from XP is going to be to an open-source clone of XP developed by a small team, that offers them no guarantees whether it works, no support, and the possibility that development could stop at any time.
If I can offer you cloud-based access to a Windows app you need that no longer runs on hardware you can purchase, you don't have to know crap about what OS I'm running.
If we skip practical part, ReactOS is great as any big community-driven project, because driving a big project is hard.