Several answers from Nordic employees state the possibility of Secure Boot and a "Root of Trust" feature:
use of ARM TrustZone on nrf52840 for secure storage/trusted region
Cybersecurity features for NRF52 chips
What is the current progress for this feature and what to expect from it? Will there be a real TrustZone implemented or do we get only HW accelerated cryptography functions?
best regards, Gregor