There's a fundamental difference
Terraform's "server" was never open-source in the first place
So you already cannot pull the move that AWS did with Elastic and Mongo
The open-source part of Terraform is the CLI, the compiler, etc
Extremely puzzling move
It means you can't provide a CI/CD pipeline for terraform as a service. Because that would overlap with functionality of terraform cloud and enterprise.
Not necessarily; only if that CI/CD pipeline actually benefits from Hashicorp's code one way or another (embed, distribute, etc). I highly doubt that Hashi would consider Gitlab in breach of their license because they have support of Terraform state in their pipelines. Classic TACOS eg Scalr and similar might be in a somewhat bigger trouble as they have to have the terraform binary as part of their solution. But even then, they can remove all traces of terraform from their product and require the user to install a docker image with terraform version of user's choice.