Thank you for coming to meta with this request and for writing this up so good!
I agree with what you said. After reading your proposed tag wiki and the questions you linked I think the tag is useful and we should add it.
A little thing I found while browsing the questions you linked, which, by the way, is one of the reasons why this is such an important step: the first one currently uses the tag figure-of-speech, which has the following tag wiki:
This tag should be used when asking a question about a figure of speech, such as when asking how to incoporate a certain type of rhetorical device in your writing or which kind of rhetorical device could help you convey your intentions to your readers.
Looking at the history I was the one who wrote that tag wiki. As you can see "rhetoric", or more precisely, "rhetorical device[s]" play a role here. I think we should update this with some of the information of the answer to "Rhetoric vs Figure of Speech" that you linked to:
Figures are a subset of Rhetoric, albeit a major subset, which is probably why you have equated the two. Nonetheless, they are different. Rhetoric is an over-arching framework for persuasive speech or writing that not only includes figures, but also includes topics like the appeals (ethos, pathos, logos), identifying the type of situation, the canons, and various other areas.
In fact the question itself could be linked in the tag wiki for either or both of the tags rhetoric and figure of speech. But your proposed tag wiki is a nice start and we can just add another edit once we have a better wording.
Here a few things about what the process from here on could look like:
- We should wait a couple days for others to chime in. Tag requests are not the most interesting thing to read, which is why it often takes a while for those interested in tagging efforts to come together - especially on weekends. I'd say on Monday around noon UTC we could simply go ahead if nothing happens here. Currently the question has been viewed 12 times - and quite a few of those are probably from us at this point :D
- We need to edit the questions that need the new tag rhetoric (needs someone with 150 reputation, though it's faster and easier if you can simply edit questions after 1,000 reputation). In order not to flood the frontpage with old questions it's preferrable to only edit a few questions in a batch and then wait a day or so before editing the next batch.
- After the first question has been tagged with rhetoric someone should propose the tag wiki edit (anyone can do that) or simply edit the tag wiki (4,000 reputation privilege).
- Later someone should edit rhetoric and figure-of-speech so that they refer to each other and the question Rhetoric vs Figure of Speech in order to make it easier for others to find out what the differences are when seeing the tags.
So, basically: let's wait and if nobody comes around until, say Monday noon in the UTC timezone, and says "No" you can just create it. And if you need help don't hesitate to ping me by leaving a comment.
Update (roughly a week later):
I created the tag rhetoric, retagged two questions with it and added a simple wiki to it, plus I added a bit to the figures-of-speech. If anyone has any more ideas you are welcome to suggest an edit.