On similar lines as Mr. Ionescu's suggestion, a separate disk could be made that includes a collection of drivers, which for binary blob/licensing reasons (or simply because including all of them would inflate the release ISOs too much) can't be distributed in the official ReactOS release.  It could be called "Windows Offline Drivers Disk" or something, nominally as a utility for people installing Windows on a computer not connected to the Internet (which can actually be a pain in the ass, especially when Windows can't find the driver to my USB WiFi adapter to connect to the Internet because Windows didn't ship with drivers for it and it's not connected to the Internet to access Windows Update but my Ethernet cable isn't long enough to go across the room and someone else is currently using it anyway), so that it has functionality with Windows systems separate from ReactOS, thus dodging the "are the drivers for Windows or ReactOS" issue.  During second stage of ReactOS installation there could be a prompt asking if the user would like to insert the Windows Offline Drivers Disk or (other media) to search for drivers.  (Or if the computer is connected to Internet the disk could be streamed from whatever site hosts it like how Download Manager does it with other apps, if that doesn't create a separate issue.)