New to ARMv8-M over ARMv6-M/ARMv7-M are low-overhead hardware-based security extensions with ARM TrustZone. ARM documentation on the ARMv8-M security extensions explain, "It defines a system-wide division of physical memory into Secure regions and Non-secure regions, and two system-wide security states that are enforced by hardware. The architecture supports the creation of a Trusted software stack that provides features such as Secure remote firmware updates, while significantly reducing the attack surface of such code. This is an important feature for any network-connected device that can be updated after deployment, including any IoT device." See that aforelinked page for more details.
With the latest GCC Git activity, various bits of the securty extensions support from the compiler perspective has landed. The work was done by several ARM Holdings developers. This work will be found in next year's GCC 7.1 release.