The thumbnail image of Hugo should be displayed at the top the article.

[diguage]

The build result:

[ahus1]

Thanks for suggesting this feature. AFAIK the layout you're asking for can't be generated by pure Asciidoctor technology, and showing the image is achieved via a custom Hugo template of the blog.

It might be possible to get a similar behavior in the preview by adding a docinfo which could include JavaScript to add the image from the information contained in the frontmatter. Again, it might be possible, and it will be definitely a happy adventure.

I'm adding a "help-wanted" label, maybe someone has the skills to tackle this. I assume I'll not pick it up soon as I'll be focusing on core features and the maintenance of the AsciiDoc plugin.