^Agreed...my thinking may not follow exactly with how it's gonna go. But my angle is that there's always the "market" limiting factor.
Not everyone who buys the A45 AMG will be a hardcore performance enthusiast, or would appreciate a jumpy powerband. It will have to be a smooth powerband, and be able to do city and track duty alike. It isn't an AMG black series...so the lunacy may not really be there in full swing (as yet)
Of course, AMG could use Variable Turbine-whatever-it's-called technology (like in the 997 Turbo) to minimise lag, but ultimately you're still limited by small displacement at some point.
So that said, I still think either the hp is gonna go down, or the engine size is gonna go up.
IMHO, euros *normally* use turbos for power (torque) band "bolstering", rather than massive power increases like the JDM's do (not sure if this statement makes any sense).