In version 4.x you can create repositories of only one specific type (maven, gems, npm, etc').
There is no need to check any checkbox to support a specific repository type, when creating a new repository, a dialog will open, asking you to select the repository type:
Once the repository type was selected, the layout will be auto assigned (if available for this repository type).
For remote repositories, the URL will be auto filled to a relevant default package type's registry, i.e: for RubyGems, the URL will be 'https://rubygems.org/'. This can of course be changed to a different URL.