Fix Compatibility Issues with Power Query (tabular metadata change causes source query to go into read-only mode)

Power Query is the method being pushed as the load mechanism for models on PowerBI. And a good thing too, PQ is probably one of the best things MS has come out in this space for a while.

But it doesn't work well with Power Pivot. Currently the development is one way. Any changes in power pivot to a table loaded via power query renders the source query read-only. I've noticed some changes in excel that stop some modifications, but changing column metadata and formatting still breaks it.

eg I generate a datetime using power query in one of my models. I forgot to change the data type to datetime in the PQ, it came into my model as a string. I changed it in power pivot so I could use it with temporal functions. I also added some other helper columns to my date dim (easier using dax vs M). Issues arose when I put it up on power bi due to localisation (i'm in a d/m/y zone, powerbi is in a m/d/y zone)
all of a sudden my "current date" is 4th of nov 2015 instead of 11 of april because the text to date conversion is occuring in the model.

It's too late for me to go back to my source power query and change the column data type to a date. I need to blow away that part of my model and recreate.

This high coupling of separate elements makes powerpivot + powerbi only really suitable for demoware and prototyping.

Having to rebuilt a model just because you want to change a column data type in the source query has put a lot of people off using this for anything except quick demos and inconsequential internal reporting