That is one of my proposals as a part of my effort to get rid of code rules that try to use the term "shall be permitted" to prohibit other methods.
3. Proposal (include proposed new wording, or identification of wording to be deleted):
200.x Common Neutral Conductors. Common neutral conductors shall not be used unless specifically permitted elsewhere in this code.
4. Statement of Problem and Substantiation for Proposal:
It appears that CMP 2 is attempting to prohibit the use of common neutral conductors by specifically permitting them in 215.4(A) and 225.7(B). There is no reasonable reading of the words “shall be permitted” that can lead the code user to the conclusion that these words actually prohibit the use of common neutral conductors in other cases. The act of specifically permitting something in no way prohibits something else. Section 3.1.2 in the NEC Style Manual says that the words “shall be permitted” are to be used to permit an alternate installation method. The words “shall not” are required to be used to prohibit an installation method per 3.1.1 of the Style Manual. This change will make the wording in 215.4 and 225.7 comply with the style manual rules. Also the prohibition of the use of common neutrals should rest with CMP 5 as they have control of Article 200, Use and Identification of Grounded Conductors and not with CMPs 2 and 4.
"It is the first responsibility of every citizen to question authority." B Franklin