You closed your question with this:
"So what's the deal here? And more importantly, is there any point in me including one in any typeface I design (assuming it isn't a Fraktur script or historical reproduction)?"
Yes there is a point. Because you have only told us, what it will not be, not what you intend it for. Typefaces are like vehicles. You would be surprised where people are taking their cars. Four wheel drive? Parked outside the opera house! Sports car with no ground clearance? Deep on the beach... So make no assumptions about your users.
Need an example?: ¦ is part of Latin-1 Supplement and Wikipedia is clueless. But I am using this as markup in a certain program (which does not handle tags) to be later processed into non-breaking spaces for rendering before printing. The beauty of this one is actually that I am quite positive that it will never be part of any text-content - and still I find it in most fonts.
In one comment you have phrased your question in a more helpful way: "what is "complete"?". You are making a typeface and you want it complete. Why not select as many Unicode blocks as you can muster courage/patience/creativity for, while thinking of your target audience. I am a user who is often frustrated when selecting a certain typeface and later missing just one or two characters for an "exotic need" (I do check my usual suspects for our languages, but in journalism things sometime come up unexpectedly.).
You better just pick a few blocks and complete those, than having holes in your typeface, which are not obvious in the online distribution-sites, because they either list typefaces by language-support or by ranges. Some allow filtering by characters but that is a hassle for customers.
Also, if your typeface turns into a succes, you can later add to it. Or afford an assistant, if you are selling it...
Also consider, that once you offer your work online, you will be "competing" with thousands of other typefaces. And the "number of characters" is always an indirect measure of quality. Why? Because design of typefaces is attractive to artistic people but is also gruesomely much work and needs patience and stamina. So when I see an offer with 40% more characters, I know that the creator has got more patience and stamina than the one next door. And I conclude that the spacing and the meta-data will also be "more nicely worked and fine-tuned".
Sorry if this sounds discouraging, I am mainly writing from the perspective of a user or "customer" and we "want it all". Personally I have never used a long s as far as I remember, but in old German texts I have come accross many, so you never know...