As a matter of fact, a 4Matic all wheel drive W205 C63 AMG prototype already exists. Check out AMG's senior powertrain engineer Dr. Jorg Gindele had to say, "Yes, a C63 is possible. There is one car already [a prototype at AMG's headquarters in Affalterbach, Germany]. I know this because it’s my car!”
If the senior engineer in AMG's powertrain development is driving around an all wheel drive C63 AMG that bodes well for all wheel drive to make it to the next gen car. He also confirmed 4Matic all wheel drive for the next generation W222 S-Class AMG.
Another interesting tidbit is that Dr. Gindele hinted that an E63 AMG Black Series is a possibility. It is not set to come or anything like that but could happen. Still seems unlikely though as AMG has yet to do a four-door Black Series.
Somewhat amusing to see AMG announcing more all wheel drive models and the expansion of 4Matic in the AMG lineup while BMW is shying away from competing.