The data model il PowerPivot and Tabular is defined using XMLA.
Having a textual representation in a Domain Specific Language (DSL) of the Tabular/PowerPivot Model would solve many open issues:
- generate difference between two models in a readable way
- easily copy/paste parts of a model into another one
- easily edit/refactor large data models with a text editor
- enable check-in check-out and team development based on a text file (merging differences made by different authors)
It would be completely acceptable reprocessing the data model once you apply differences.
At the minimum, an "official" Language should be defined so that third-party and communities tools would use a common standardized language.