The official answer from LEGO is this:
"There will be a download available later this year with the programming blocks you need to use legacy sensors and motors. There will also be a service item available online with the hybrid wires you need when connecting a legacy sensor/motor to the NXT."
Come on, now... admit it - did anyone actually think that LEGO would hold this from us? I think not...
Thank you, LEGO, for the official answer AND for making it a good one!