Update: We had a bit of a misunderstanding on the update text. As commenter Gardner points out, the restart and other options on the power button menu were in the SHIELD Tablet 5.0 update. The "SHIELD Power Control" menu, a section of the primary Android Settings menu that was included in KitKat but dropped from the 5.0 update, is back in 5.0.1. Sorry for the confusion.
Inside the SHIELD Power Control menu are basic settings for the Tegra K1 processor and a few screen options, as well as more standard Android settings like a sleep timer for the screen and Wi-Fi.