I am leaning towards YAML for this.

Just a general note.  During my last job (in a lab mostly frequented by psychologists, linguists, etc.) I wrote a suite of modules for EEG/ERP analysis, and my general conclusion was that if you make the user interface too complex (as is unfortunately sometimes required for generic solutions), people simply aren't going to use the tool — in particular, if the entry threshold is high, and it doesn't come with lots of ready to use cut-n-paste examples.

In other words, using YAML would be fine if they know it already, but otherwise they might not be willing to learn it  (which could mean - at least if you work in the same lab - you'll always be the one eventually writing the code for them :)