I think what AK needs depends on what the goal is for the park. If its to be a true stand-alone for the masses, worthy of a full price one-day ticket, it definitely needs a full land, maybe 2, with 2-3 E-tickets, and 8-10 B-D's. (Admittedly, these numbers are not based on any type of scientific study, but rather are pulled out of my ear as I head into a conference call...).
But if the goal is for it to be a supplement to the other three, one that attracts guests for a 1/2 day here, and a 1/2 day there, and only the die-hard animal lovers pay full price, then it is nearing completion. Or at least its nearing a state of adequate completeness, if that makes sense.