This is a topic that came up among the mods and admin a while back. The general opinion back then was if it related to TES then fine, otherwise we weren't so keen. Mainly because we might end up with a huge amount of non-TES stories posted.
Personally, my opinion is that if TES fans are likely to enjoy it, then thats fine. The tricky bit is deciding what qualifies and what doesn't. There have been a few non-TES stories put up that we've allowed, but if every 3 stories (for example) was non-TES then I think there'd be a problem.
My advice... pm Stargle and ask his opinion.
p.s. Oh, and Revan. Your idea I don't think would even need running by Stargle, I think it would be fine. It still has a connection to the Elder Scrolls world.
p.p.s. Sir Radont, I've read "Fallout" and think it would make a fine addition here. Regardless of the outcome of Star's decision it won't be about the story. It's just whether he thinks it's advisable to open up the forums to such a potentially wide range of different genre's. If he asks my opinion...well, I think you know what that is

But then again, I'm a sucker for a good story. Worst comes to worst, add a link to your sig.