Are there aircraft exemptions for CPDLC in the NAT area?
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.