If this is a legitimate basis for refusal, it should not apply in cases where the proper refusal is merely descriptive or generic, which should be stated expressly in the guide. Beyond that, the guide does not provide any guidance on what the distinction is between "incapable" versus "merely descriptive," "generic," "ornamental" or "use as a mark."
As noted by others, saying that the matter "merely  imparts information" or "conveys an informational message" is inadequate because all trademarks "impart information." To say that "These types of incapable informational matter do not function as marks because, even when used in the marketplace, consumers would understand the wording to convey information or an informational message rather than as a mark to indicate a single source for the goods/services offered under the wording" is entirely circular and therefore entirely unhelpful.
The examples in Appendix B appear to show that there are a number of different applications of the refusal, some valid, some not, and for the most part overlapping with other already-existing bases. One category appears to be the manner of presentation, not the content of the mark itself. A number of the examples are ornamental (e.g., Clothing Facts, I [heart] DC) and others are used in a non-dominant fashion, i.e., not as a mark (e.g., "hours of energy now"). Assuming that something in addition to the the existing bases of ornamentality and use not as a mark is needed, the examination guide does not solve the problem because it doesn't describe the basis for refusal in terms of the style of presentation.
Other examples are clearly generic and should have been refused on that basis, not an ambiguous "incapable" basis. These include perhaps "think green," "best dad ever," and "once a marine, always a marine."
Perhaps one gap is for terms that have had widespread adoption, and thus are incapable of exclusive appropriation by any one entity. The BOSTON STRONG application is an example of this, where the phrase was so quickly used in so many ways it was incapable of being exclusively owned; the Bible quotes and other news-generated tropes would presumably be the same. If this is the need this guide is meant to fill, describing the refusal as based on use that is too widespread or ubiquitous to be capable of adoption as a mark is a rationale with much clearer contours than saying it is "merely informational."
In summary, the latitude to refuse a mark because content is "informational" is not adequately distinct from the statutory bases of merely descriptive and generic, or the well-accepted basis of ornamentality and use not as a mark. It only gives the Trademark Office the opportunity to refuse registration on ill-defined, ambiguous grounds, and an applicant will have no way to rebut the refusal because of its lack of specificity. If this category is necessary at all, the occasions for its application must be much more clearly defined that simply "informational."