Proposed resolution (October, 2015):

1. Change Clause 15 [cpp] paragraph 1 as follows:

group-part:
if-section
control-line
text-line
# non-directive conditionally-supported-directive
...
non-directive conditionally-supported-directive:
pp-tokens new-line

2. Change Clause 15 [cpp] paragraph 2 as follows:

A text line shall not begin with a # preprocessing token. A non-directive conditionally-supported-directive shall not begin with any of the directive names appearing in the syntax. A conditionally-supported-directive is conditionally supported with implementation-defined semantics.

[Adopted at the February, 2016 meeting.]

The Standard needs to describe non-directives more fully, e.g., whether they are ill-formed, conditionally-supported, etc. Since they are, in fact, directives, a different name might also be in order.