Filtering by category (or adding contacts by category) is something we have had in mind for quite some time, and should indeed increase usability with large contact lists.
As it is now, the plugin can only be instantiated once (and the name of the file it opens cannot be changed). But by simply supporting multiple instances, each associated to a different "data file" or a different "contact category", it should be possible to achieve something similar to what you suggest.
We will see...
Thanks for your feedback and ideas!
