Many thanks for asking this. Doing Astro Pi with NASA is something we would absolutely love to do. There is the possibility of ESA promoting Astro Pi to all members of the ISEB (International Space Education Board) of which NASA is a founding member, but I am not sure the status of that currently.
I also notice you're a HAM, same here (M6DNT). We have also undertaken a collaboration with ARISS who intend to fly another Astro Pi unit to the ISS to become part of the HAM TV rig. The has potential for a whole new kind of ARISS school contact where they could run student code on the ISS during the live contact with the crew.
Sorry I don't have anything more concrete than this, but watch this space!