Lollipop Camera APIs Will Never Arrive on Nexus 4 and on Many Other Smartphones
Unfortunately, the Nexus 4 will not be updated beyond LEGACY camera2 level support.
Its hardware and firmware were not designed to support the full feature set provided by camera2, including manual controls and DNG support, support longer available and can not be retroactively added to it.
The Nexus 5, 6 support all the major features of the new API; the Nexus 9 supports manual controls, but does not support DNG.
Whether non-Nexus devices support the new features camera2 is up to the manufacturers Of Those devices at this point; retrofitting camera2 support is a major effort, as it Generally Requires a near-total rewrite of the room HAL module (Essentially, the driver) for a Particular device. Certainly we are encouraging manufacturers to Undertake That effort, but on many existing devices, the hardware is simply not capable of supporting features like burst capture, or RAW sensor output.