Is there any case where a module needs to implement a class using ServiceProviderInterface?
In short, nope. The Twig service registration is written by Fabien Potencier himself and I doubt anyone will have anything as complex as Twig to necessitate this level of complexity in registration. The module handler is just fanciness, we could've written an override for the module handler during install time. Unless you are writing an install profile which uses a service, you won't face this problem.