The 6.3 AMG engine is quite a beast - unfortunately, MB/AMG is now shifting over to a turbo 5.5 litre engine (cleaner on emissions, improved MPG) while still badging the cars as "6.3".
Odd move since AMG designed this engine from the oil pan on up on their own and now after introducting this in the '08 models, it only had a three year run. Very expensive to retire a new model of engine in a short run like that. The prior AMG models had MB engines that were modified for AMG applications, so the basic tooling/development piggybacked on the 'standard' engine legacy costs.
There's a couple of '11-'12 models that will use the 6.3 NA in smaller body styles, due to lack of space to fit the turbo and exhaust plumbing, but that's a stop-gap measure until those models undergo a full redesign in future years.