An Nvidia employee has confirmed a Pro edition of Nvidia's streaming Shield Console, to be released in May close to Computex. The console will come with Android TV in the Pro as a normal version with Tegra X1-soc.
The Pro edition will get 500GB version has been confirmed by ManuelG, an Nvidia employee active here on our forums. It's also noted that the console will support Netflix, and if it can do Ultra HD that will come in handy for a lot of people. The regular Shield console will get 16GB of NAND capacity. The Pro version was rumored after it appeared and disappeared real fast on amazon.
You should not expect any further differences other than storage capacity in-between the regular and Pro model. As stated both streaming consoles will run Android TV and work with the GRID streaming service. These boxes will get a Tegra X1 soc with four Cortex A57 and four Cortex A53 cores. The embedded GPU is Maxwell based with two smm units and a total of 256 stream/cuda/shader processors.