I posted a feature request: Field Type Template Suggestions to allow us to have #field_type template suggestion and preprocess functions in core.
At the moment you cannot override something like all taxonomy reference fields or all image fields, you are limited to field_name, bundle and field_name__bundle which are all groovy but not the raw down-low grunt needed when you want to simply override all fields of a particular type.
A particularly ugly example of this in D7 are taxonomy reference fields which are spat out DIV's (uncool eh?), actually this is how I discovered this whole debacle - trying to make every taxonomy reference field a list. Not possible in core...
So, please, if you have an angle on this head over to the issue queue and lets hear it, I think this will be of much interest to themers - remember this goes way beyond just taxonomy reference fields - there are many field types and I can see D7 sites have many many fields.