I need to think about this
The way the plugin works is that get all users and then filter to remove hidden users etc.
I could add to the filter to check if the use is part of custom post type
Here is some that I might be able to start from
But I would what to extend to to support multiple custom page types
And if this is set is this an only or add option
so we might need to have 2 options
just_post_types="dddd,page" and add_post_types="dddd"
This will need to be added to the options as well as the shortcode handler
I will see if I can poke at the code and let you know how I get on
Ping me if I haven't got to in a couple weeks