I personally believe Biom group 2 will be the ones who will be exempted from biometrics, because everyone who is in biom group 2 have -
1) Given biometrics this year itself (2020)
2) Are inland applicants (FSW-inland, CEC)
3) Its a guess, but i think people in this group haven't left Canada after giving biometrics.
This means verifying the identity of biom group 2 people is easier without the biometrics as they gave it earlier and have been here in canada since then.
Disclaimer - All this is just a theory based on what I am observing.