The ioXt Alliance, who is working to “build confidence in IoT products”. have recently released a requirements document (they call it a Pledge) that mentions some HW and Platform Firmware requirements, including Secure Boot:
Click to access ioXt-Pledge-Book_S.pdf
https://www.ioxtalliance.org/the-pledge
PS: It is just me, or are all the images on this web site larger than most? 🙂