From my point of view, with the rise of 3D printing / additive manufacturing, Rhino and Grasshopper are getting more and more traction from the mechanical engineering community. Therefore, i guess it makes sense to now start thinking about interfaces towards CAD tools like CATIA, NX, SW and so on.
I think it is important to think about specific workflows. For instance, an engineer may not want to model everything from scratch within Rhino/Grasshopper. He may start creating the part structure and assembly structure in a conventional CAD tool and then on some regions she/he may work on sophisticated design patterns within Grasshopper and dynamically re-import them back into the CAD tool through a STEP file. Or another workflow may be to generate the geometry in Rhino/Grasshopper and then export the geometries for analysis to highly advanced CAE tools for FEM/CFD/MBD simulation.
In this respect, an improved STEP support and the Rhino.Inside strategy are very elegant as it lets Rhino/Grasshopper spread like a virus into different tools and workflows. This is already happening with tools like Revit, Blender, Unity and so on.
From my point of view, with the very open and developer friendly approach, McNeel is creating a very strong platform for geometry generation in different applications. I have tried programming in different conventional CAD systems but usually the languages are old (e.g. VB.NET), you require additional very cost-intensive developer licenses, there is lack of modern API libraries, and most tools do not really have an active developer community. Moreover, I am not a friend of purely cloud based solutions because they do not allow creating more advanced automated workflows as the tools cannot be controlled via batch or run on a server/cluster.
Curios to hear the opinion from other people working in the field of mechanical engineering.
// Regarding your question: One non-invasive approach to integrate Rhino/Grasshopper into different CAD systems could be to use journal files and macros (e.g. to quickly important and export STEP files and communicate between Rhino/Grasshopper and a certain CAD tool).