void Finalize(JSObjectRef object);

The finalize callback is called on the most derived class first, 
and the least derived class (the parent class) last.

You must not call any function that may cause a garbage
collection or an allocation of a garbage collected object 
from within a JSObjectFinalizeCallback. This  includes
 all functions that have a JSContextRef parameter.

typedef void (*JSObjectFinalizeCallback) (JSObjectRef object);

This API did not meet the test objectives. Furthermore research for a working prototype providing proof of work performed using this callback interface did not produce any conclusive results. WebKit developer's have been notified of this issue, but since it is highly important, and they failed to meet production parameters in this instance, the best case scenario is to go forward with the Global Allocator object approach, to keep track of allocated data.

This is not a drawback, its actually a benefit. We are separating the interface from the implementation, thusly we can be as robust and stupid as required for a general application profile.

A segmentation fault can occur with any native procedure that expects a value that can be converted to string or number, but the value is not converted to string or number, resulting in a null pointer being passed to a procedure or set of statements that may not be able to accept one. This is likely to happen when uncaught exceptions are thrown during value conversions.

JSE doesn't 'already' handle these issues, because these happenings are how we learn how the engine operates in the real world.