Certain trends seem almost unstoppable while the current Costcos are changing the shape of the market in ways that add new dimensions to future stores.
Size is the fundamental trend.
No matter how you look at it, as long as people embrace Costco then they also embrace size and conglomeration. Bigger stores, more stuff. But Costco is by no means the final stage, there is still lots of room to expand. Automobiles, entertainment, hardware, etc. There are many markets that Costco had not yet fully exploited.