The trick with a suspended railway is the limitations that you have. A loop is simple enough if you want curved or straight sections, but the points/switches would need to be new designs. The existing track options (regular L-gauge rails, monorail, roller coaster track) are all designed to have the train above the tracks and don't make way to have a train suspended below.
I could see if you designed a new car for the roller coaster track that would cling to the sides/bottom of the rails, using the existing rail pieces upside-down.
Otherwise, would want to see a box-section track, something that could easily be connected to supports that would be clear of the suspended trains. Points/switches would be a very nice thing to have, to build beyond a very basic layout.
If LEGO makes new parts or the community here designs a new system it would be great to have an option to motorize it. Train sets are more fun if you have the option to run them on a motor.