XAutoload 7.x-5.x now has full support for PSR-4 as in Drupal 8. So, you can now organize your module class files in Drupal 7 like this:
class: "Drupal\$module_name\Foo\Bar" file: "$path_to_module/src/Foo/Bar.php"
"Drupal\$module_name\Foo\Bar"
"$path_to_module/src/Foo/Bar.php"
Enjoy!