I'd say that this should be left to user-mode translators (eg,
something like QEMU but for Windows/ReactOS). Most Windows
applications are currently built only for IA-32, it's hard to find
things compiled for other platforms (Win64 is gaining popularity, but
still...).
Running ReactOS on a platform in which Windows as limited or no
support already, such as SPARC or PowerPC, does indeed leave the user
practically left in the dust in terms of compatibility. However, most
users will likely be running ReactOS on x86 or AMD64, so in-kernel
translations of binaries will just add bloat that most users will
never need. It's my opinion that if any project is made to run
non-native binaries (like what QEMU on Linux does), it really should
be left in the user-space, as an optional thing to run, but does not
add any bloat to the core system itself.
--
Mike