The maintenance effort.

The big performance win is nice (this benchmark:

https://github.com/rjpower/falcon/blob/master/benchmarks/mat...

), but it is still going to be a lot slower than doing it the horrible way (calling out to Numpy).

The benchmark is more aimed at demonstrating the reduction in loop overhead than it is at numerical speed, but numerical stuff is usually where you end up with a lot of loop overhead...

It'll never happen, CPython is the reference implementation and a change as drastic as rewriting all of ceval.c is too drastic for any point release.