DLO,
I use a number of criteria for judging submissions for inclusion in Stellar Reaches. Here's what would help you get the best chances of being published (aka, this is what I look for):
1. Length: Try to aim for 1-8 pages. Longer, and it is harder to justify the space. (I have made exceptions, though I prefer not to.)
2. Applicability: The more people that can use the material, the better the chance of getting published. Make sure that you write it from the perspective of making it useful to the most people, and that will go a long way.
3. Compatibility: The more compatible your work is with a published rules system (or multiple rules systems, if possible), the more people can use it, so that's a major consideration.
4. Self-Editing: The less work I have to do to edit and prepare something for publication, the better your chances of seeing it. If I have to do a lot of work on it, then it only goes in if I have the time and inclination to do the work.
5. Most Importantly, Interesting: If I don't find it interesting, it's likely I won't think others will. Aim for interesting, as it makes for a good read. (The whole Alternate Universes concept is based on the fact that people like to read snippets about interesting backgrounds that vary from the OTU. Interesting goes a long way with me.)
6. If you set your work in the OTU, stick with canon as best as possible.
I've published prestige classes for T20, so I'm pretty sure I'd be interested in looking at a well-done advanced character generation system for Athletes.
Let's see what you've got, my friend,
Flynn