See discussion here: http://markmail.org/message/gmpmege2jpfrsp75. Both docFreq and totalTermFreq are already available to the TermsComponent, it's just that doesn't add the ttf measure to the response.
This issue adds a new terms.ttf parameter which if set to true results in the following output:
The reason for the new parameter is to not break backward-compatibility, though I wish we could always return those two measures (it doesn't cost us anything, the two are already available to the code). Maybe we can break the response in master and add this parameter only to 6x as deprecated? I am also fine if we leave it and handle it in a separate issue.