I'm no transportation planner, but I designed this based on MTA's current East-West Connector. Charlotte BRT would start at Davidson Road where a fairly large Park & Ride could be sited (plenty of land for sale here and easy access to I-40) and continue along Charlotte going through West Nashville neighborhoods, passing through the medical district and then approaching the North Gulch before making a loop in the downtown core, going north around the Capitol and then swinging south on 4th Avenue, then Demonbreun, then 8th. The line would then pick back up on Charlotte before you cross the Cumberland where the route would remain unchanged. Adding the downtown core loop allows for access to businesses, entertainment, and of course the convention center without cutting down Broadway and disrupting pedestrians and the honky tonk scene.
Here is MTA's proposed East-West Connector
Here is what a BRT system could look like on Charlotte Ave: