The NVIDIA SHIELD is powered by their Tegra 4 SoC and runs "100%" on Google's Android, so the code drop isn't exactly a huge surprise. NVIDIA characterizes the SHIELD as an "Open Gaming Platform" and "an open ecosystem where any developer can develop and release content that takes advantage of SHIELD's features. SHIELD is one of the first Android devices to allow game developers to create top quality content that can be enjoyed on the big screen in the living room as well as a mobile experience."
NVIDIA hopes that encouraging their customers to develop for the SHIELD device with 5-inch display will work in bringing new software experiences to the device. NVIDIA also continues to promote the SHIELD's ability to stream games from the GPU to the device and console-quality development tool. The open software project around the device is aptly named Develop For SHIELD (Develop4SHIELD).
There's also a new NVIDIA blog post on Hack Your SHIELD.