Downside with that is having DNS, managed databases, cloud storage (s3) outside K8s - When deployments are also managed with tf, it's easy to connect a deployment in K8s to resources outside K8s (via tf state).
You can still do that by reading the values you need directly from the state file. I suggest that you define outputs and access them through the state file from other projects, otherwise the external dependency will be hidden.
It depends on your use case what the best option would be. You can put variables into kustomize templates and replace them via envsubst. For helm charts you can just supply the values for the variables during the install / upgrade.
Another possibility would be to create a ConfigMap with the values you read from the state file.
