I think I understand:
- Partials are dumb when it comes to “output formats” (Hugo uses the extension to determine text or HTML parsing, but that is another story)
- This is not a problem inside regular templates (in fact, it makes it plenty flexible).
- For shortcodes, see https://github.com/spf13/hugo/issues/3220 – this issue is in progress and will give a solution to the AMP “amp-img” etc.