Interesting. Two miles down is a ways though. What if something went wrogn down there? Still I would want to go down and check it out.
The ocean is a harsh environment. A lot to consider given it's corrosive nature, the extreme pressures, etc. Overcoming the technical challenges would be expensive, as well as maintenance (i.e., keeping the barnacles off), however, the price/availability of land in Japan is probably real expensive and thus may make it viable one day. I would be concerned about building it near the "rim of fire." Nevertheless, I too would be interested in a tour.
"Uh, Mr carter, we have a problem with the # 8 filtration pipe, there is something stuck in there. We are going to need you to swim down and check it out." LOL