Not currently possible in the existing plugin. Yes, possible with additional programming, so you have posted this in the correct place as a feature request.
Please note, however, that there are a couple of crude work-arounds:
1. Simply create another position for each location, and add each member from that location to that new “position” (as well as any other positions they hold). You could call it something like “All Seattle Team Members”, and then it would show up as a selection in the contact form.
2. You can also add a location argument to the contact form shortcode, so you could set up different contact forms for each location that only show members from that location in the select list.
I realize that neither of those are ideal, and #1 would clutter up the directory quite a bit more, but that’s the best I can offer for now until such time when or if I decide to add new features to the plugin. So, we’ll leave this here among all the other feature requests, just in case I get motivated to add more features at some undetermined point in the future, or if some other developer wants to contribute and is looking for new features to add.
Location was a feature that was added somewhere down the line after I decided to release this plugin publicly. We didn’t need a Location feature for our school PTA, which is what this was originally developed for, so the code is not in place to email all members of a specific location, especially since that feature is optional (so locations may or may not even exist).