Formatting support on HN is bare minimum, the only options here are italic text (two asterisks) and codeblock (four-space indention), and there's nothing more. It's very unlikely that Hacker News will add any new styles, since the minimalism is intentional, which can be a bit limiting. However, you can use plaintext mailing list and forum traditions for everything else (e.g. manual blockquote mark ">", deletion mark "^H", sarcastic mark "/s", new subsection mark "- title" or "* title", etc). I usually use the more readable HTML <del></del> markup for strike text. Of course, Unicode abuse is always possible, just like what you've did here...
Only one thing to beware: To make a newline, you must make a new paragraph by creating an empty line (e.g. "line1\n\nline2"), merely a "line1\nline2" doesn't work. Just like LaTeX or Markdown, a line break in the source code is not the same as a logical paragraph in the output, it makes sense, but the lack of other formatting options makes it a bit inconvenient to making a list. But it's tolerable in the end.
test
test
__test__