Add the option for audiences to be joined by an AND instead of the current ANY (OR) for targeting.
As default, ANY audience that matches will be included in the experiment. However, you may want to use multiple audiences to avoid having to create weird hybrids.
Example: A campaign targeted to mobile phones
Audience 1: All mobile devices
Audience 2: query param = your campaign
If you had an "AND", we could use these two audiences (thereby being able to always have a reusable mobile device audience). However, at present, we would have to create a 3rd audience that has both the mobile targeting AND the query param.