In section 3.1.3 the oa:Motivation class is, actually, not used by itself. Looking at the vocabulary it is of course clear that the specific instances listed in the table are instances of that class, but this fact is mostly unseen (and unused) by most of the users.
I think it is better to remove the reference to oa:Motivation from that section, and formally refer to it in Appendix D, where motivations are extended. That appendix should be marked normative for that to happen.
Ivan
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Ivan Herman, W3C
Digital Publishing Lead
Home: http://www.w3.org/People/Ivan/
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ORCID ID: http://orcid.org/0000-0003-0782-2704