The main issue is developing device drivers is very complicated and difficult to get right. A sensible approach IMO would be to have ReactOS run virtualized on top of the Linux kernel. That way Users get all of the stability benefits of Linux, plus hardware support. The ReactOS team would then be able to concentrate on Windows compatibility, while only developing a few drivers for virtualization. The downside with this approach is a huge performance hit on computers without virtualization extensions. However I think the main use case of ReactOS is to provide a way to run old windows programs on modern hardware, so I don't think this would be a concern for most potential commercial users.