I've got no idea. Conceivably they could come out with a new approach and transition Workflow to it by having it support both mechanisms. That might be easier to do and be less disruptive to users if the app is in-house. But even if they do introduce a new mechanism, existing apps would still have to adopt it which would take years.
So absolutely Apple could introduce a new mechanism, but their buying and encouraging adoption of Workflow is a strong indication to me that they have no intention of deprecating the URL mechanism any time soon.
I agree here. If they do have an idea for improved inter-app automation or "dialogue", this would be a great example case and implementation of it. Plus this team's knowledge in this field could help guide what's needed, and also help out with Siri stuff to do on-the-fly "workflows".
So absolutely Apple could introduce a new mechanism, but their buying and encouraging adoption of Workflow is a strong indication to me that they have no intention of deprecating the URL mechanism any time soon.