I think the idea is correct, but hard to retrofit, you sort of have to have it there from the start.

Objective-Smalltalk runs on the Objective-C runtime, so Objective-Smalltalk methods look like Objective-C methods accessed via objc_msgSend() to the entire rest of the system, including to other Objective-Smalltalk code.

That means it doesn't really matter to the rest of the system if any particular method is interpreted, AOT-compiled or JIT-compiled. They can't tell, except for execution speed.

And of course the execution model includes machine primitives, which the interpreter also deals with but doesn't make faster, but the native compilers do.