A volume meter displayed on the UI of the mobile app during a stream, which is color coded to display clipping issues. Follow the standard green / yellow / red color scheme alongside the actual decibel count. This would be very useful for people streaming on mobile in loud venues such as conventions. A persistent input volume monitor would allow the broadcaster to maintain a quality stream by adjusting his or her microphone volume to match the situation.
I stream live music performance and writing, and find the mobile app great for quickly setting up a stream with an acoustic guitar and vocal. The only (slight) difficulty is getting my device set at just the right spot. Getting the entire scene in frame, reading chat, and making sure I'm not too close to the mic can be tough depending on the environment and circumstance. A dynamic volume meter and quick access to volume adjustments would be very helpful.