For them to get accepted into the CNCF would require relicensing a large amount of MPL work. What's always been confusing to me about Hashicorp's change and any subsequent relicense of OpenTF is that I know for a fact not everyone who contributed code to Terraform signed the CLA and allowed permission to relicense.
I suspect if OpenTF tries to relicense to a more permissive license like Apache 2 (rather than less in the case of BSL) license we might see some fireworks.