(Disclosure: I'm from Digger and OpenTF so am biased)
Hashi's biggest miscalculation is that they put Terraform (an open language / ecosystem) into the same bucket as Vault and Consul, which are hostable backend applications.
BSL makes sense for Vault, just like it does for MongoDB. It is reasonable to prevent others from charging for hosting your code.
But with Terraform, the backend part (TF Cloud) was never even open source. And it's not required for Terraform to work.
Hashi shot themselves in the foot. Unlike with Vault or Consul, there is enormous vested interest in the community to keep Terraform truly open. Hashi trying to enforce everyone to use their non-oss backend with it will only result in Hashi losing the privileged (and well deserved) position among providers of commercial products in the Terraform ecosystem.