I have never had Sushi prepared with brown rice.  Somehow it seems wrong to me.
That certainly sounds non-traditional, but it's probably a little healthier for you.
The lacto-fermentation of the rice prevents fish from spoiling. In one Asian dish, narezushi, salted fish was stored in rice for months at a time.
That's pretty crazy. Is that a popular dish today?
I'm not certain, it was the earliest form of sushi and probably originated with paddy fields along the Mekong river.