Dev version of Twigify. (Requires drush.)
Install/enable this module in your Drupal 7 site and run the command drush twigify. Twigify will return a list of currently installed themes that it can convert to Drupal 8.
After Twigify has written the new converted theme to your Drupal 8 installation you will need to clear cache before enabling it.
Please report any issues or feature requests in the issue queue**
(**aka the "wish you queue" as in– I wish you would add this feature.)