Only hard sci-fi.

It's not disallowed, but it has never been common or very popular here.

I'd thought that Usula K. Le Guin's "The Ones Who Walk Away from Omelas" might have been an exception, but though it's had nine submissions, it's only ever earned single-digit votes, and a single comment:

<https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...>

Far more success in comments:

<https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...>

(I thought I might have first encountered it here, though it might have appeared elsewhere.)

Harlan Ellison's "I have no mouth and I must scream" has had some success: <https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...>

Marshall Brain's "Manna: Two Views of Humanity's Future" (2003) was what I'd had in mind when finding the Ellison story, but it's also had little success:

<https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...>

Cory Doctorow's Little Brother by comparison did well: <https://news.ycombinator.com/item?id=6390441>. Though still hardly spectacularly.

E.M. Forster's "The Machine Stops" has seen both multiple submissions and comparatively decent discussion: <https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...>

(Searching specifically for fiction is something of a challenge, I'm trying a few different queries as they occur to me.)

I suspect both length and copyright limitations work against fiction submissions generally.