Adobe has thus far released two CID-keyed OpenType/CFF fonts that use the special-purpose Adobe-Identity-0 ROS ("ROS" is an abbreviation for /Registry, /Ordering, and /Supplement, which represent the three /CIDSystemInfo dictionary elements that are present in CIDFont and CMap resources): Kazuraki SP2N L (かづらき SP2N L) and CJK Type Blog articles, the most recent of which being the May 9th, 2012 article.

The big question that may be on a font developer's mind is under what circumstances is it appropriate to use the Adobe-Identity-0 ROS?

The answer is surprisingly simple:

If the glyphs correspond to one of the public ROSes—Adobe-CNS1-6, Adobe-GB1-5, Adobe-Japan1-6, or Adobe-Korea1-2—or a subset thereof, then using a public ROS is recommended. It is never a problem to build fonts that include only a subset of the glyphs in a public ROS.

Otherwise, the Adobe-Identity-0 ROS is a better choice.

One advantage of using a public ROS is that existing resources can be leveraged, such as CMap resources, GSUB feature definitions, and so on. When using the Adobe-Identity-0 ROS, these resources must be created. The March 7, 2012 CJK Type Blog article details how to build UTF-32 CMap resources, including an example for the Adobe-Identity-0 ROS.