He still wants to do a school of Banggai Cardinals. He has to make a new fish model with extra geometry (3D points) to handle its extra complexity.
Jim will definately wait until after the 3D Background. The 3D background will have a completely rewritten fish avoidance and so a school of Banggais will be much easier to handle.
You see, right now the Aquarium is on two planes.
The fish can either be on the Front layer or the Back layer, or they can be in transition between the two layers. Also, the tank isn't very deep.
In the 3D background version, there will be either several layers of depth, or unlimited resolution of depth. This is so fish can freely roam without having to struggle so much to swim around each other as they do now. Jim has done an excellent job masking this limitation, but you can't do eels and jellyfish with a 2 layer "short tank" setup the way it is now.