Drupal8 is pretty awesome, but its a problem that you cant choose fromt the ui which template to use.
Sure you can overwrite whats there (node--article.html.twig) but that dont give the end user a chance to later change in the site & can end up in even more templates & clutter.
Make it easy to provide a template suggestion for entities, blocks, pages, nodes, fields, menues, username, everything that have a template you should be able to give a suggestion.
A prepopulated list of classes that can be selected for a template.
The modules userbase is sitebuilders & themes that wants to provide variations for a site, developers dont have to provide templates after a site is build, and can rely on the theme to provide all the variations.