The latest updates to the Android 4.4.3 AOSP changelog include references to two new Nexus devices (via Android Central). The first is the “Flounder” tablet, which was also recently referenced in builds of Chromium. This is likely to be a tablet or a phone, as Google has historically used fish-related codenames for such devices.
Perhaps more interesting is the mention of the “Molly” set top box. This device would likely be one of the first Android TV products to hit the market. The “Molly” box is listed as being built by Google, instead of an OEM partner, which means that it might be considered the successor to the ill-fated Nexus Q.
project device/google/molly/ e610c57 Set BT minor code to SET_TOP_BOX instead of HIFI.
Few details are known surrounding either device, though they may well be revealed at Google I/O in June.