If you want to suggest it, why not make it happen it yourself? Personally, I'm in the process of editing a Naruto rationalist fanfic written by a friend of mine. I'm also a former Mage player with some knowledge of the Mage universe (though to be honest I'm more familiar and experienced with Ascension than I am Awakening), so I'd be happy to look at a draft of a Mage fanfic before you post it if you so choose, or else I'd certainly read it and review it once you post it.
The problem is that I am not myself a rationalist, so I wouldn't be any good at writing it. Mage: The Ascension is not particularly good for rationalist fanfiction, since it takes place in a universe where consensus reality is true, and thus the scientific method fails as a way to understand the universe, since the laws of physics are determined by how many people believe in them.
Furthermore, the reason I bring this particular fandom up is because the other fans continually tell me that in the game world, rationalism and the scientific method are wrong, ev...
I've been enjoying reading Less Wrong fanfiction, and I wanted to suggest another fandom that should have at least one rationalist fanfiction: Mage: The Awakening. It's a roleplaying game about "modern sorcery." My description can't really do it justice...