If I read the page correctly - and I am NOT knowledgeable about the topic - the CPDLC is not used for approach control, which is the issue in NYC and DC. The example uses given are oceanic routes and above FL195 or FL285. It mentions "continuous descent approaches" as a future possibility.

Isn't approach one of those times where 1) you don't want the pilot distracted by more visual information (instead of audio), and 2) pilots listen to exchanges with other pilots to keep situational awareness?