The new Mercedes-AMG GT is a different segmented car as the SLS. It will compete against the Porsche 911, Aston Martin Vantage and Jaguar F-type. These car all have a roadster version as well, so Mercedes needs to make a topless version as well
The new Mercedes-AMG has a 4.0 liter V8 engine and will have a higher weight due to more steel to strengthen the chassis. The roof will, like the SLS roadster, have a cloth roof.