Let's start with casual stereotyping of people: Finns know how to be silent in five different languages.
That's me circa 2000. Easier to remain silent rather than say anything out of the fear of making a stupid grammar mistake and looking stupid. Roll half a decade forward and I had gotten over staying quiet... but not in writing.
Around that time, I got somehow interested in fanfiction: first by reading, then actually writing some myself. This actually coincided with another thing: I was finishing up with Elder Scrolls 3: Morrowind (Bethesda Game Studios/Bethesda Softworks/Ubisoft, 2003) and taking up modding it.
If you've played that game, you know it had a lot of text. It didn't have voiceovers either: outside of very few situations, all dialogue was just text with hyperlinks to new topics. That made creating quest mods easy. Well, easier since there was no need for voiceovers etc. But that still required being able to write believable dialogue. Create a believable plot. Write the mod so to avoid game-breaking sequence breaking. Naming OCs do not steal. Avoiding words like "LOL" or "oh em gee" and paying attention to grammar.
My first mod was... bad. The dialogue was stilted, the plotline full of clichés and overall the content was barebones as anything. But I'd like to say me writing fanfiction made me become a better modder... and vice versa. By writing dialogue for my fanfiction, I learned to write dialogue for the mods.
While I still can't create good characters and worlds of my own (my aborted attempts in creating webcomics would stand proof of that, if I ever got beyond mental post-it notes with them), I finally learned to write dialogue better than what a player would tell the computer to do in an 80's text adventure ("Go east. Eat chicken."). The short books I wrote into the game also helped me develop as a writer.
And finally, when it came to writing my final work in English at the university, being able to write English at a decent speed helped a lot in making the transition to writing technical text that had some kind of flow to it and wasn't thoroughly plagued by grammar issues and typos -- just like my blogs here. Of course, my betareaders had also helped a lot in this learning process with fanfiction.
In the end, my ambitions exceeded my skills, so I gave up on modding. I didn't have the patience to build new locations with more than the bare minimum of garnishment. I didn't know how to create new armor or textures, not that I would've found those interesting. Indeed, that line of thinking is exactly why this cblog doesn't have any images in it either.
So fanfiction is to blame for me having written all the blogs I've written on Dtoid with my half-decent English. But now we're getting to my main point in the blog, if I didn't signpost it clearly enough already:
Aren't content mods for a game analogous to fanfiction for noninteractive media?
The modder borrows the canon from the original game. So does a fanfiction writer. Both expand the world beyond the original in some sense -- unless the mod is a total conversion.
The mods I wrote for Morrowind were sidestories to the Nerevarine's journey. But so were all those mods that added rings of healing that regenerated player's health at a level that broke the game or ridiculously overpowered weapons.
While there is plenty of awful fanfiction, there also are plenty of awful mods. Maybe the threshold to open up a game editor (and getting it to output a mod) is higher than opening Notepad and starting to type in a story fit for Bulwer-Lytton fiction contest by accident (competitors try to write the worst possible opening sentence for a novel), so the overall level might be better.
But the similarity isn't limited to just the writing and the creation of a new plotline, or how experience in one helps in the other.
The Super Mario Maker (Nintendo, 2015) levels people like Blonde Bass created -- that's fan-created content, new stories in Mario's repeating journeys to find the right castle. The only difference to fanfiction that I can see is that you're not only brought along for the ride, you're in control of the ride.
I don't know how to find a mod comparable to Harry Potter and the Methods of Rationality. But to find an equivalent of the infamous My Immortal, all you need to do is just start up 100 Mario Challenge.
(EDIT: What a misstep this blog was. Eh, better own up to my mistake of repeating what is obvious and more or less said in the Bloggers Wanted prompt already.)