I started to write a new firmware which runs python. Actually it should only run compiled python programs (the ones from CPython) due to memory restrictions. I'll use PyMite, a python VM for embedded systems, which already has nice support for AT91SAM7S256. For the base OS and hardware drivers I'll use NxOS since it has very clean code and it's easy to create new kernels with it.
I'll also try to keep the USB/Bluetooth interface compatible with the one of the LEGO firmware and I'll use the same file formats for image, sound, melody files, etc.
Nevertheless I don't really know how fast this will run and how big programs could be. So this will be rather experimental. But I'm very optimistic and for as a python fan I just can't wait to run some python code on my NXT

Preliminary project name is "PythoNXT" short for Python on NXT. At the moment I haven't done very much, except setting up a development environment and writing a simple test program combining PyMite and NxOS. Now I first have to wait for LEGO to replace my NXT, since my display is broken.