This is amazing, and obvious in retrospect. Gradual compilation can be adopted, well, gradually, without breaking existing code. 100% upside, 0% downside. PyPy team should consider making this delivery mode the #1 priority. Even worth reconsidering the object management impedance as well, and go for 100% compatibility with CPython object model. I suspect this would have a small runtime cost, but a would be a huge boon for smooth risk-free adoption.
Back in Python2 days, you just slam "import psyco" and your code magically goes faster. The pysco authors went ahead and invented pypy.