"... is really suggesting (1) that the world needs people who specialize in multidisciplinarity (if that makes any sense) because (2) these people make the knowledge in the disciplines usable. In other words, orators draw from specialized knowledge whenever they need to and to whatever extent they need to in order to do something in a public venue. I could be reading into Cicero here because I'm projecting my own hopes for liberal arts, but it seems like this goes a long way toward explaining and perhaps validating the "dappled discipline" we talk about so much." - Tom Sura, 2008
Word to all of the above. For me this sounds very sensible; it is a way of advocating for being able to move between discourses, which is vital for understanding (and most certainly in an orator), and, make connections between the conversations. This is one of the reasons that every time Socrates got all up in Rhetoric's face about being not connected to a skill I became frustrated: part of its job is making the connections. What is a body when the bones are not joined to muscle are not connected to skin? That sometime subtle connective tissue is important. So, word.
I would draw your attention to the end of the section that you point to though (XXXI this is testing my Roman number knowing...):
"If the speaker or writer has but been liberally instructed in the learning... at the same time, has chosen the most elegant writers and speakers to study and imitate, he will never, be assured, need instruction from such preceptors how to compose or embellish his language..."
This is a very interesting point for me: if we give them a good liberal arts ed, they won't NEED EXPLICIT INSTRUCTION in RHETORIC (Gasp comp teachers)! Interesting. I think that this is curious, because in some ways, it makes some assumptions about how the teaching would take place. The way I see this kind of liberal education working is with a WAC focus, in which the students are learning how to write and talk about their subjects as they go from the teachers who are working with them, as part of learning the subject. Of course, at this point in history there is likely one teacher working with you who is giving you everything... kind of the ultimate WAC. I wonder also if the liberal education that is being advocated for the orator would also include reading all those Greek texts that Plato and others wrote... thus gaining instruction on oratory, and philosophy, and sinister and lengthy banter all in one go?
This statement about explicit instruction brings to mind talk about ending comp classes, about students needing to read and practice writing more... rumor that they not only don't "get" what we are trying to "explicitly" instruct them in... they don't care. If they just had to read and write and speak publicly more, in all of the subject matter they were asked to cover... would comp even be needed?