What will the 737 MAX 7, 8, and 9 ICAO IDs be?
The new Boeing 737 MAX is based on the Boeing 737 Next Generation family, which it will replace. Also note that 737 MAX is still under development and is scheduled to release in 2017.

Update:

(Source)

The first 7 is omitted and the suffix is now an M for Max, e.g. B37M for the Boeing 737 MAX 7.

Wikipedia has complete list of ICAO codes here.



ICAO Aircraft Type Designators: Search for Boeing and you will find 737 MAX in the list.