I considered doing this, and have some of it implemented. I discussed it with Larry Hastings and Mark Shannon at PyCon Ireland, and we decided to just use ''.format() and the new FORMAT_VALUE opcode, since that was the simplest way to fix the previous implementation's faults. That doesn't mean I've given up on improving it, of course.

The speed increase would indeed come from avoiding the LOAD_ATTR lookup, not building list, and not calling a function.

I'm curious about your benchmarks. Can you share them? I've found f-strings to be typically faster than .format(). But I can't say my benchmarks are particularly awesome.