Definitely doable to "open up" Music Plaza for general guest use. It's a massive space that takes away a good amount of real estate.
Universal can easily afford smaller acts that can rotate throughout the night in 30-45 minute intervals to provide add'l entertainment. It may not be an E-ticket house, but it's something.
House 1 enters by BMG restrooms, exits by Fallon restrooms.
House 2 enters by BMG/Rockit (Bloodmoon), exits by Fallon restrooms.
House 3 enters at Fallon, exits by Fallon restrooms.
House 4 & 5 enters at new Festival Center area (not to scale), exits at Festival Center 2.
*Assumes they can use the BMG hallway/breezeway.