NVIDIA tends to be very diligent when it comes to upgrading its first-party Android hardware. Earlier this month the company sent out an over-the-air update for the SHIELD Tablet, bumping the mostly-stock software up to Android 6.0 Marshmallow. A day later it halted the update, because early users were reporting that the new software made the tablet's Wi-Fi inoperable... which is kind of a big deal, especially when most of your tablets are Wi-Fi only. Today the problem has apparently been fixed, and the update is being resumed.
The news was posted on NVIDIA's official forum, which remains quite active. An NVIDIA representative says that "we’re confident we have corrected the problem and are releasing a new Software Update." The latest update should now be available for the original SHIELD Tablet and the slightly revised SHIELD Tablet K1, as software version 4.0 and 1.2, respectively.
The NVIDIA update doesn't add much on top of the AOSP upgrades in Marshmallow, though it does include a few new branded wallpapers and a revised camera app. NVIDIA tends to make its updates available to all devices at the same time, so users probably won't have to wait on a rollout period. The US LTE version of the SHIELD tablet will be updated later.