Get capabilities/APIs available to the current user or tenant
Microsoft Graph abstracts out different services into the single set of APIs, but in practice some services may or may not be available for particular user or tenant.
For example, Azure AD accounts without Office 365 do not have access to /me/people API (Outlook REST API), this API returns 404.
Currently there's no way to determine what capabilities or APIs are available without trying to call the API and handling the error.
Knowing such information in advance would make it possible to build user experiences adaptive to what's available.