Place the dried black mushrooms and soybeans into 2 separate large containers and cover each with several inches of cool water; let stand 8 hours to overnight.

Rinse and drain the mushrooms and soy beans. Trim tough stems from mushrooms; cut each mushroom into halves.

Bring a pot of water to a boil. With a sharp knife, cut an X shape into the peel of each chestnut. Add chestnuts to the boiling water; cook until hot, 3 to 4 minutes. Drain and plunge immediately into a large bowl of ice water to stop from cooking further. Drain and set aside. When cool enough to handle, peel the chestnuts from the shells and discard the skins and peels. Set the peeled chestnuts aside.

Bring 16 cups water and long-grain rice to a boil in a large pot. Reduce heat to medium-low and cook at a simmer for 30 minutes.

Heat oil in a wok or large skillet over medium-high heat to 400 degrees F (200 degrees C). Cook and stir bok choy in hot oil quickly, about 1 minute; add to the rice.

Stir peeled chestnuts, black mushrooms, soy beans, water chestnuts, red dates, and salt into the rice. Bring the mixture to a boil, reduce heat to medium-low, and simmer 30 minutes. Stir chicken into the rice mixture, bring again to a boil, reduce heat to medium-low, and simmer until chicken is no longer pink in the middle, about 10 minutes.