Update: March 18: Launched.

Indications from several sources (including our own) indicate that the iPhone 5c is set to see an expansion tomorrow with a less-expensive, lower-capacity 8GB model. But that might not be the only Apple iOS device announcement for tomorrow. According to a source, shipments of Apple’s fourth-generation iPad with Retina display have been arriving at Apple Stores with notices to not open until tomorrow (images below)…

KGI last month forecasted that the 4th generation iPad would replace the iPad 2 in Apple’s $399 low-end 9.7-inch slot. It appears that the transition might be happening tomorrow.

The fourth-generation iPad includes the thicker iPad design introduced with the iPad 2, A6X processor, and a five megapixel camera. The device was originally introduced in October 2012 alongside the first iPad mini, and it was discontinued upon the launch of the iPad Air last fall. 16GB versions of both Wi-Fi-only and LTE-compatible in black and white color options have begun hitting stores.

With the $399 iPad 2 seeing extreme supply constraints, it seems likely that this fourth-generation model is designed to re-ignite iPad growth at the $399 price point and it will replace the aging iPad 2. The iPad 2 remains Apple’s last tablet with the legacy 30-pin dock connector, and the return of the fourth-generation iPad would bring Lightning parity across the Apple tablet line. With the 8GB iPhone 5c incoming tomorrow (in all of 16GB/32GB colors), perhaps the iPhone 4s will see discontinuation as well.

This reshuffle would mean that the entire Apple iOS device lineup would be Lightning-only, allowing Apple to drop the 30-pin standard on almost all of its products.

Update: We’re hearing the LTE 16GB model will cost $559, that’s $30 higher than the $529 price point of the current 3G iPad 2. We’re also hearing it is possible the entry-level iPad 4 will cost $449, which is $50 more than the iPad 2 of today (update: oops, those were the iPad 4 EOL prices as of yesterday. It’s $399.