Linking Production Launch code to DTM is really helpful and a thoughtful feature. One less hassle to handle.
If there is a possibility to enhance the linking functionality, we recommend to build the same linking functionality to Staging environment in Launch and DTM as we have it in production.
This way, clients do not need to go through the hassle of deploying Launch embed code in their development environments for this migration. It would be an extra consistent approach to production, if we have the linking capability for 1 matching DTM and Launch testing environment. E.g. DTM Staging. Then, when the clients are ready to totally use the Launch embed code, we could deploy it to all environments including dev, staging and production.
Meanwhile, as we currently do not have this feature, we use Fiddler, Charles, or Requestly to replace the DTM staging environment code with Launch embed code for testing. just FYI.