We're planning to stay 100% backwards compatible, and in the early stages we definitely want for it to be easy for people to migrate back and forth between both

We're planning to stay 100% backwards compatible, and in the early stages we definitely want for it to be easy for people to migrate back and forth between both tools - even have teams with different engineers using different tools. DSL changes are honestly the thing we'd like to limit the most, but as long as they're backwards compatible, the RFC process will welcome them, and they will be discussed and considered! The important thing is for features to be opt-in. You should be able to limit yourself to a feature-set that is Terraform-compatible, if you want. If you want to use additional features on top of that, then that will be an option as well - we definitely want to innovate.