I'm a big fan of the pluggable jit strategy (I even gave a brief presentation about it at an earlier pycon). the idea is that you identify the seams in the interpreter where the jit interacts with the main interpreter loop, and then provide a clean mechanism for the built-in jit to be replaced by something else that works with the same api surface. it's a bit harder than letting the built-in jit be tightly coupled to and intertwined with the rest of the interpreter but certainly not far harder, and the work to get this sort of clean separation will help keep the jit maintainable even if there is never a second jit.
