Access custom metadata through global variables

The documentation does not state that you can access custom metadata via formulas, so it's pretty safe to assume that you cannot do so. For Visualforce, you could use Remoting or Remote Objects, and for Apex Code, you can use regular SOQL.

I have some new information

I know this works (API 41):

<apex:outputLink value="/{! $ObjectType.Your_custom_metadata_type__mdt.KeyPrefix }/e" target="_blank">Your Custom Metadata Settings</apex:outputLink>

As does this:

{!$ObjectType.Your_custom_metadata_type__mdt.Fields.DeveloperName.Label}

So I think, yes, you can use globals to access your Metadata type records in the same way as normal objects.