I don't know the details of BSL, but can HashiCorp now require compensation/$$$ from Spacelift, Scalr, Env0, etc? In that case, these products can be forced to offer similar pricing as Terraform Cloud.
IANAL but I believe the BSL restrictions only apply to new upstream code versions. All HashiCorp repos can and always will be usable under MPL as they were up until the moment immediately before the license change.
In other words: if you hard fork now, you don't need to pay.
In other words: if you hard fork now, you don't need to pay.