Update: Some readers have noted that selection of the new CPU and storage options on the low-end model does not seem to register with the online store system. Typically, changing options results in live updating of the price and shipping estimates during the configuration process, but changes to the CPU and storage are not having that effect. Consequently, customers are unable to place orders with these new custom configurations on the low-end model.
Update 2: Within minutes, Apple has now pulled the new configuration options entirely, once again leaving RAM as the only available onboard hardware upgrade for the low-end model.
Update 3: There are now conflicting reports on whether or not the new options have been pulled. Many readers are reporting still seeing the options and are able to add the configurations to their shopping carts, while others viewing the same pages are not seeing the new options.