Quite a good point there.
I know that the dynojet wideband 2 kit (with lcd display) allows datalogging and can take into account the o2, tps and at what rpm, it is basically a road dyno without giving you a power output.
And as promised, here is the pic of the dynojet screen (my phone is a nokia 6120c):
http://www.dynojetwb2.com/