Maybe it's easier to use composer.json to conveniently update the libraries with each release?

{
  "require": {
    "google/recaptcha": "^1.3",
    "matthiasmullie/minify": "^1.3"
  },
  "config": {
    "vendor-dir": "Libs",
    "optimize-autoloader": true,
    "preferred-install": "dist",
    "sort-packages": true
  }
}

Well, I agree it would be a much better solution. However, as you know, currently both of those "libs" reside in /Sources which means we can't manage them with composer.

There is nothing stopping from changing the location and specifying other paths in the source code, as in the case of moving the Languages folder. For example, let it be Sources/Libs, then the code in Autoloader.php will look something like this:

spl_autoload_register(function ($class) {
  static $hook_value = '';

  static $class_map = [
    // Some special cases.
    //'ReCaptcha\\' => 'ReCaptcha/',
    //'MatthiasMullie\\Minify\\' => 'minify/src/',
    //'MatthiasMullie\\PathConverter\\' => 'minify/path-converter/src/',

    // In general, the SMF namespace maps to $sourcedir.
    'SMF\\' => '',
  ];

  require_once __DIR__ . '/Libs/autoload.php';

... and a small change of composer.json:

"vendor-dir": "Sources/Libs",

Also, nothing stopping from placing the Libs folder in the root of the forum.

I just checked both options.