[LegionMammal978]

Yeah, if you're starting with, say, a heavily object-oriented program, then it would be nigh impossible. But I don't think it would even be extraordinarily difficult, if you start with a style that isn't suffused with dynamic function calls. E.g., languages like C++ and Rust with heavy monomorphization can have callbacks and other fun things without any vtables or function pointers.

From an architectural standpoint, the main challenge is layering everything properly so you don't have any circular dependencies, even in untaken branches. Again, how hard this is to achieve depends on the original design, but it's not like circular-dependency-avoidance is something that no one's done before.