My opinion about the "primarily opinion based" close-reason is probably a little bit different than yours about it, and from the fact your question from 2015 did get only one answer which did not directly oppose your question's statement, I would not conclude that you have broad consensus here on how this close reason should be used. In fact, my opinion about it is more in accordance to this meta answer, which says we need that close reason for questions
which are simply impossible to answer because there isn't a general answer
where suitable answers are all value judgments that will be different for each person, each company, each background.
(but are otherwise clear, on-topic and not too broad). This answer also suggest agressively edits to such questions to save them / get them reopened.
What does this mean for the question in stake?
Let's analyse the four main topics of the question one by one:
Is it purely due to legacy reasons why displaying text on our video terminals is done with ANSI escape sequences and not another framework such as JSON, Yaml, XML, or something else?
This is somewhat opinionated, but probably answerable. I gave a comment about ANSI being a standard, not writing a full answer, but at that time I already had my doubts if that question was answerable in full.
Is ANSI escape sequences in video terminal, simply an old technology similar to say, X11 that sticks around solely due to how embedded it is within the computing paradigm?
Same as above. Let me add, the wording of these sentences bothers me. It gives me the impression the OP thinks those "are only those bloody, crap, quite unimportant legacy reasons" hindering people to invent something better. To me, it looks the OP underestimates here the value of mature standards.
If not, why don't developers switch from an escape sequence style to something that would support nesting?
That is definitely something one would require a crystal ball to write an answer and falls under my personal definition of "too opinionated". We cannot read the minds of all developers all over the world, only speculate about it, but as you know, SE.SE is not a discussion site. The sentence contains also a pretty wrong allegation, that that this ANSI escape style is quite popular today, as we also discussed in the comments. Lots of developers use a kind of formatted text description which supports nesting, however the platforms for this are not called "terminal interpreters", they are called web browsers.
Are there any proposals to do away with ANSI escapes in terminals and replace it with something else?
That is something I don't know (and off-topic, since it is a request for 3rd party resources.)
Does looking at the two (good) answers change my mind on this? Not really - I can see the flaws very clearly with or without looking at the answers. Interestingly, none of the two answers adresses directly any of those four sentences above, they adress directly the wrong assumptions in the question, nothing else.
We actually don't know what would have happened when Robert would not have closed that question so quickly, maybe we would have gotten lots of more (opinionated) answers, interpreting the question differently. Maybe the community would have closed it, maybe not, who knows? But just because the explanation of the "primarily opinion based" close-reason mentions the tendency of attracting a certain kind of opinionated answers does not imply we (or the mods) always have to wait until this actually happens.
What about our expectations about how the mods should deal with such a question, which partly answerable?
I see four different ways of dealing with it, especially for a mod:
ask the OP kindly to edit its question and tell him/her what should be improved
edit the question agressively
close the question immediately.
wait what the community does (and maybe decide to close the question later).
All of them can be legitimate.
During the mod election phase, Robert Harvey clearly stated he would like to become a mod to get a binding vote to quickly close questions. Netherless he got most of the votes for his application - so it seems the community here prefers this moderation style where someone quickly closes even borderline questions.
This is actually not my preference, I would often prefer a different handling (as I have stated here). So closing the question so quickly is probably not something I would have done, since I think it contains a lot of interesting parts and may be improveable by an agressive edit to the point where it can stay open. However, I don't see Robert's action as a clear abuse of the system (as you called it more than once), it was a IMHO legitimate, understandable action - maybe not the best possible one.
To the point of not reading the answers here first: yes, I agree to you, a mod should have had a look at the answers first before closing a question, especially for questions like this one. But if they decide not to do it, it is IMHO mediocre, maybe weak moderation style, but still not an abuse of the system. And I doubt that for this case a look at the answers would have changed Robert's point of view (but let us wait what he has to say about it himself).
So is all what happened here ok?
No, there is one thing which I miss here: if mods get asked about the reasons for their actions, especially here at meta, I expect them in person to write an answer and give an explanation.
Advice #3 from stackexchange's theory of moderation says:
Whenever possible, try to leave frequent comments on posts where you’ve taken (or considered taking) a moderator action, explaining the reasoning. This is important so that community members can learn the norms of the community and the moderation policies.
So @RobertHarvey, you have been around here in the last 48 hours, but still no answer from your side? Same for this one where the OP asked for clarification about the closing, or suggestions for improvement, and you wrote not just one word about your motivations? Or this one, where you left it over to GlenH7 to give an explanation, but not even a comment if that is also your point of view? Also this one, where you left it over to gnat?
I would like to encourage you to rethink your style of (non-)communication over your mod actions. More detailed replies could actually prevent such emotional reactions as the one we saw here from David Arno which lead to such excessive accusations of "abusing the system".