The JS-API provides the 'plumbing' to the REST APIs which will allow you to create the UI components for managing users, groups and permissions. The ADF roadmap does include managing permissions via pre-build UI components, you'll see this work starting to appear from ADF version 2.3.
Dashboards, and Dashlets are not Share features on the ADF roadmap at the moment, however all the pieces are there which will allow you to create custom pages with dashlet style components. You could even create some reusable components and contribute them to the ADF project: GitHub - Alfresco/alfresco-ng2-components: Alfresco Angular Components
There is an Open Source project, released at the end of last year, which is not designed to replace Share but is to demonstrate how to create a file/document app using the ADF, a sub-set of the Alfresco Share features. You can get code from here: GitHub - Alfresco/alfresco-content-app and even contribute to the project to help us progress it faster. Version 1.1 of this project is expected mid-March.