Example with overriding HtmlWebpackPlugin params to templateContent function and compilation instance manipulating

extract-stats.js

import { remove } from 'lodash';

const MANIFEST_CHUNK_NAME_REGEX = /.*manifest\..+\.js/;

export default function (templateParams, compilation) {

    const stats = {
        styles: templateParams.htmlWebpackPlugin.files.css,
        scripts: templateParams.htmlWebpackPlugin.files.js
    };

    const manifestChunkName = Object.keys(compilation.assets).find((asset) => {
        return MANIFEST_CHUNK_NAME_REGEX.test(asset);
    });

    if (manifestChunkName) {
        stats.manifestContent = compilation.assets[manifestChunkName]._value;

        remove(templateParams.htmlWebpackPlugin.files.js, name => {
            return MANIFEST_CHUNK_NAME_REGEX.test(name);
        });

        /* eslint-disable no-param-reassign */
        compilation.assets['stats.json'] = compilation.assets[manifestChunkName];
        compilation.assets['stats.json']._value = JSON.stringify(stats, null, 4);
        delete compilation.assets[manifestChunkName];
        /* eslint-enable no-param-reassign */
    }

    return { assets: stats };

}

template.jade

// This trick gives us ability to write pure template files:

doctype html
html
  head
    each filePath in assets.styles
        link(rel="stylesheet", href=filePath)
  body
    #app

    if assets.manifestContent
        script !{ assets.manifestContent }

    each filePath in assets.scripts
        script(src=filePath)

webpack.config.js

// ...
plugins: [
  new HtmlWebpackPlugin({
    templateContent: compose(indexPageTemplate, extractStats)
  })
]
// ...

Hi, this is just a first step but maybe you can go from here alone - feel free to ask for details :)

plugins: [
  new HtmlWebpackPlugin({
    template: 'extract-stats.js'
  })
]

Now we can use the power of the compiler:
extract-stats.js

  // This function has to return a string or promised string:
  module.exports = function(compilationResult, chunks, assets, compilation) {
      // Play around with the arguments and then use the webpack jade loader to load the jade:
      return require('./template.jade)({assets: assets});
  };

@jantimon

this function will receive only first argument :(

function(compilationResult, chunks, assets, compilation) 

https://github.com/ampedandwired/html-webpack-plugin/blob/master/index.js#L212