2 things prevent this right now:
As it turns out, EventMachine no longer works on Windows and will be replaced by the already finished Arachni::Reactor, which will be released along with v0.5, if not sooner.
The v0.5 codebase runs on Windows but communicating with phantomjs for some reason is slow to the point of being unusable.
The aforementioned behavior was caused by a silly DNS issue on MS Windows. Once fixed, performance was satisfactory. :)
Still much slower than on *nix, but fair.
Good news all in all.