[pfdietz]

Tangentially, I think the future of optimization in CL and similar languages is run time optimization/compilation. For example, the goal should be to make (typical cases of) generic function dispatch as fast as inlined structure field access, even in the presence of the possibility of redefinition of the functions and classes. This is not easy, since these may get redefined while calls to functions using them are on the stack.

[User23]

Since code is data, some kind of functional persistence might be the right path forward here. I lack the expertise to develop the idea further though. I don't much care about the exact behavior vis-a-vis functions on the stack, so long as it's well-defined.