It comes up from time to time. It is unlikely the site would change. One could add it locally however if they have uBlock Origin in their browser then one way to add a dark mode would be going into the uBlock Origin settings -> My Filters and adding

    # HN dark Mode:
    news.ycombinator.com##body:style(background: black)
    news.ycombinator.com##td:style(color: #fafafa !important)
    news.ycombinator.com##table:style(background-color: #24273a)
    news.ycombinator.com##div.toptext:style(color: #fafafa)
    news.ycombinator.com##div.c00:style(color: #fafafa !important)
    news.ycombinator.com##a:style(color: #ffa000 !important)
    news.ycombinator.com##span#karma:style(color: #faa000 !important)
    news.ycombinator.com##span.pagetop:style(color: #fafafa !important)
    news.ycombinator.com##textarea:style(color: #696969 !important; background: inherit; )
    news.ycombinator.com###hnmain:style(background: #24273a !important)
    

Adjust color hex codes as desired. There are a few elements missing in this one, I would have to look for the other version but this should be a start.