Would it be possible to add to ability to create "Singles" and "Global variables"?

Hi! This is actually possible today using the Structure Builder API. You can follow this tutorial to set it up: https://www.sanity.io/docs/create-a-link-to-a-single-edit-page-in-your-main-document-type-list The reason we have gone with this approach is that in many cases you want more instances of your “singleton documents” once a project matures and grows. For example, you have a “settings document” for a website, but then you want to add a second website property to your Sanity project. Then you can opt out of the singleton configuration and support multiple settings documents with the same fields.