Nvidia has announced that they have released the Shield's Operating System for anyone to tinker with. They hope that hackers and software modders of the thriving Android modding community will take up the challenge of developing for the console.
The Shield runs a stock version of Android, which means that there will likely be a lot of headroom and different directions the modifications can run off into, the forum at XDA-Developers will be the best place to keep an eye out for mods. With the Shield having very powerful specifications, it remains to be seen what can truly be achieved with the Tegra 4 powerhouse contained within.
If this all seems too good to be true Nvidia do mention that the warranty policy will allow them to reject returns on devices that have been rooted, or where a bootloader has been installed, but they go on to say that "Our goal here isn’t to discourage people from rooting their devices – it’s yours, after all – but to give us a course of action if folks start to abuse the hardware through software modifications".
If you want to learn more about developing for the Shield you can find out more at https://developer.nvidia.com/develop4shield