It is...
It is eloquently described on the CAST Web site as follows: "NIMAS guides the production and electronic distribution of digital versions of textbooks and other instructional materials so they can be more easily converted to accessible formats, including Braille and text-to-speech." The key words in NIMAS are simply accessibility and flexibility.
The limitations of print and the barriers it poses to those unable to use print can and will be eliminated. Different people have different reading needs, and a NIMAS file can be used to output whatever accessible format a student may require, regardless of reading challenge.
As a subset of the DAISY/NISO Standard, NIMAS does not provide the markup complexity and 'richness' that is inherent in DAISY/NISO. But provision of NIMAS files by publishers to organizations producing accessible materials does mean consistency in source file format based on the international DAISY/NISO for these organizations.