Are there aircraft exemptions for CPDLC in the NAT area? Another question lists the aircraft that are exempt from the EASA CPDLC rule.

Is there a similar exemption for aircraft operating in the North Atlantic?
There will be no exemptions for the CPDLC rule in the North Atlantic Track area. 

The Datalink Mandate will be implemented:


starting 5 February 2015: FL350 to FL390 (inclusive) on all tracks within
the NAT Organized Track System (OTS)
starting 7 December 2017: FL350 to FL390 (inclusive) throughout the ICAO
NAT region.
starting 30 January 2020: FL290 and above throughout the ICAO NAT region.


ATS Surveillance Airspace, airspace north of 80°N and the New York FIR are excluded from the mandate. 
This means that aircraft equipped with a suitable transponder / ADS-B transmitter will be able to cross using the Canada - Greenland - Iceland ADS-B corridor without having to carry FANS 1/A equipment.