A question somewhat similar to the ethernet vs. Ethernet question that piqued your interest popped up ages ago in connection with the World Wide Web words internet/Internet and web/Web. See Should the words "internet" and "web" be capitalized? A later question that asked only about internet/Internet was closed as a duplicate. See Capitalization of "Internet". Neither question was accompanied by significant research—as was often the case in the earliest years of this site—and the first of the two questions remains open.
Strikingly, the answers given to these two questions are very nearly obsolete, as, over the past decade, the world of publishing has shifted strongly toward lowercasing both internet and the web (and webpage). A carefully considered, up-to-date answer citing current reference works and formatting preferences would be quite useful to EL&U on the internet/Internet and web/Web questions, in my opinion.
I suspect that ethernet/Ethernet is a similar case—but it's difficult to gain a hearing for it because of EL&U's one-two punch of (1) don't ask a question like this without showing your research, and (2) if the reference work you consulted answers the question, why shouldn't we close the question as general reference?
The most straightforward path forward would be to reopen the question as one of inherent interest (7,000 page views in five years) that isn't particularly well served by a rote application of the "show research" requirement (both Merriam-Webster and American Heritage treat Ethernet as referring to a particular proprietary protocol or family of protocols that, therefore, should be initial-capped; but even 20 years ago, the word lists at the computer magazines that I worked for distinguished between narrowly specific Ethernet and generic ethernet—and I doubt that the generic sense of the term has diminished in more recent years). But reopening the existing and keeping it open would require persuading any number of close voters NOT to apply their usual standards to a question and NOT to leave the factually dubious but appealingly forceful and concise one-line answer to the closed question in place as the only EL&U answer to the closed question. That would not be easy to do.
To pose a closure-resistant question such as ethernet vs. Ethernet on this site, you would have to cite multiple reference works that disagree about the answer, or you would have to cite reference works that say one thing and usage data that point in another direction. That's asking a lot of a typical question asker who may not know where to look to find the components of a detailed and reasonably comprehensive answer.
Regrettably, EL&U's institutional position is that the best way to distinguish a good question from a bad one is to require the question's poster to present a bunch of research to prove the question's worthiness. I don't think that this works, and I think that it causes a lot of perfectly reasonable questions to get closed for reasons that have nothing to do with their potential usefulness to future site visitors. But it's the world of English Language & Usage as we now know it, and I don't expect it to change anytime soon.
With regard to your specific questions:
1. My meta question is, if closed questions can't be answered, why is one of the choices for rejecting edits to a closed question that the edits should have been a comment or an answer? Is it simply to prevent low-rep users, who cannot comment, from attempting to reopen questions?
The canned argument asserting that you should have submitted a comment or answer instead of editing the question was almost certainly formulated without any thought that someone might use it to reject an edit of a closed question. Rather, the option was devised to thwart attempts by editors to mess with open questions rather than responding to them in a comment or with an answer. The fact that this particular canned rationale for rejecting an edit doesn't make sense as a practical matter when it is directed toward someone who can't respond to the question with a comment or an answer BECAUSE IT'S CLOSED is merely incidental fallout from the site's heavy dependence on prefab rejection reasons.
2. Should I ask a separate meta question if I wanted community feedback as to how to appropriately reopen the Ethernet question specifically, given that I genuinely think there's an underlying question there, which hasn't been answered in other sources and is appropriate for ELU?
I don't think you need to ask your second question in a separate posting. The issue of how much revising an editor should do to make a closed question reopenable has been contentious at EL&U. Some site participants vigorously oppose any effort to put words in the mouth of the original poster, which they consider presumptuous and disrespectful of the poster and of the integrity of the question that doesn't meet the site's guidelines for remaining open but by God does say what the original poster wrote down. Other site participants are more sympathetic to your inclination to see certain closed questions as imperfectly expressed but worthy of rehabilitation through clarification or refocusing.
My advice, however, is to start over with your own new question, marshaling enough visible evidence of research to avoid the closure Scylla and enough contrasting or conflicting data to avoid the closure Charybdis. What you (probably) don't need to worry about, if you do those two things, is that someone will come along and say, "Hey this is a duplicate of that old question about Ethernet vs. ethernet that we closed five years ago! Let's close it as a duplicate!" Logically, you shouldn't have to worry about that happening because, whereas the ethernet/Ethernet question from 2016 was closed for lack of research, you will have provided sufficient research to jump safely through that flaming hoop. But of course—as we saw with the Catch-22 recommendation that, instead of editing a question that you can't answer or comment on, you should answer or comment on it—logic doesn't always win the day. Good luck!
