4K Video Recording with the Camera2 API In the Android Lollipop, Google released the Camera2 API.

Does this mean in Lollipop, any phone with a 5MP camera would be able to shoot 2K video and any 13MP camera would be able to shoot 4K video, and is there any reason why Google may not choose to include this in the Google Camera for Lollipop later this year - ie would shooting in a higher resolution be a compromise in any way?
No, the camera sensor resolution isn't the only factor that determines whether a phone can shoot high-res video, regardless of the APIs offered by the OS. Phones have special video encode hardware to make a video file from the raw camera data, and the hardware can only encode so many pixels per second. To record 2k or 4k video, the video encode hardware has to be fast enough, and other parts of the system need enough bandwidth/throughput to handle the data rate.

As for Google Camera, there's no point speculating about its future releases. They might choose to focus on a new feature instead, or may wait until more phone hardware supports 4k video. They might even include it in the next Nexus phone but wait another six months or so before releasing the feature more widely.