I still don't really understand the advantage of ReactOS in any particular situation, although I suppose if you really liked NT-era Windows (and people do) it's a re-enactment society for that.
So it's not about ancient Windows NT 3.5. ReactOS aims compatibility (Win32 apps and drivers) with more modern Windows versions.
I can install XP on a VM and get away with a few GBs of space; the last time I tried Windows 7 instead, the space occupied started to grow uncontrollably, even after making little changes.
Or what we will see instead is the status quo support or not from Microsoft. There are plenty of 9x machines out there.