You guys gotta remember that the SFML Game Jam is not limited to C++, any language is allowed as long as there exists a SFML binding for it.
The most popular binding is probably C#. You know this binding quite well, do you see any portability challenges? How well does Mono work on other platforms?
Concerning other bindings, it depends how many people are actually interested in them, before making a huge effort for nobody. I'd say people that use a binding should announce it beforehand so that it's possible to think of a way to run the game on as many systems as possible.
Come on guys just build for ms windows and be done with it.
Have you considered the possibility that not everyone might own a Windows operating system?
Also, since SFML is a portable library, I don't see why we should exclude other platforms. Let's rather find a solution to ease the cross-platform build process.