Don't get too excited. It's not like nvidia are actually opening up here:
The scope of this work is strictly limited to Tegra (although given the similarities desktop GPU support will certainly benefit from it indirectly), and we do not have any plan to work on user-space support. So do not uninstall that proprietary driver just yet.
This is only about leveraging the hard work already done by nouveau hackers, in order to bring their embedded SOC product to market more quickly. There was no documentation dropped, and they're specifically refuting the idea desktop linux support.