Your theory regarding PyPy's JIT is disproved rather easily. Python's grammar has been shown to not be context free. This implies that in the best case, the parser is supralinear in both time and space. Just the parser. Now add the rest of the JIT.
My hand-waving is "disproved" even more easily than that, by passing a dynamically generated string to `eval`. However, that's missing my point (and my "-ish"): the JIT is a constant overhead. Assuming they're being careful to not dynamically generate code for handling each coroutine (seems like an obvious thing to avoid, and a reasonable assumption), the JIT'd code is shared across all coroutines, so as you accept more and more connections, requiring less memory for each coroutine will eventually outweight the memory cost of the JIT.
