How to compare / diff WF .xaml files

It's surprisingly difficult to define the notion of "difference". If you can define it strictly and perhaps also define how it should be represented, I'll probably will be able to give you some idea. The programming part of it would be simple enough...

First of all, I would warn you against using existing file differs or their algorithms or even criteria. You can use them, but this is not what you want. You really need logical, not textual difference.

—SA