Can the D compiler detect final and optimize?

[IGotD-]

A little bit related to that some want class methods to be final 
by default just like in C++. If I'm not mistaken one benefit of 
final as default is that the compiler will insert hard coded 
branches to the method as well as the possibility to do inlining. 
Are my assumptions correct?

Instead of having final as default, can't the compiler itself 
infer when a class is implicitly final and do the optimizations 
itself? Benefits would be that a programmer has the possibility 
to extend about all classes (in C++ would only be possible if 
class author makes all methods virtual). The final keyword would 
just mean that a class method is not allowed to be overridden.

Is this possible at all?