Great blog (again) Markus!
Maybe good to mention is that the Cloud-ready mode is now based on native Fiori apps and the CMP Process model (as in data model) and with that leaves the Web Dynpro FPM screen technology and the 'classic' data model with e...
Nice example of a use case that MDG suits perfectly given it's workflow based processes.
On the solution;why not use the BAdI: Calling of System Method for Rule-Based Workflow instead?
That way you will be upgrade and future proof in case SAP will ...