From April 15, you can enable line numbering in some wikitext editors - for now in the template namespace, coming to more namespaces soon. This will make it easier to detect line breaks and to refer to a particular line in discussions. These numbers will be shown if you enable the syntax highlighting feature (CodeMirror extension), which is supported in the 2010 and 2017 wikitext editors.
From April 29, it will be possible to suggest values for parameters in templates. Suggested values can be added to TemplateData and will then be shown as a drop-down list in VisualEditor. This allows template users to quickly select an appropriate value. This way, it prevents potential errors and reduces the effort needed to fill the template with values. It will still be possible to fill in values other than the suggested ones.
More information, including the supported parameter types and how to create suggested values: . Everyone is invited to test the feature, and to give feedback on this talk page.