Note: This question is somewhat open-ended and prompted more by curiosity than any sort of actionable problem or idea. It seems to me like an interesting discussion topic, but if people view it as unclear what I'm asking, too broad, or off-topic for any other reason, I will understand.
The question came to mind while I was thinking about tchrist's question: What can be done to bring up site quality?
I'm both interested in the perspective of users who have been here for a long time, since the early days of EL&U, and in the thoughts any user has about how a site like this moves through different stages.
As with any topic, there are some questions about English that are "frequently asked." They are the questions that many people wonder about and search for online. In the "grammar" branch, many of these questions are addressed by sites that write content seeking search engine traffic to promote their brand or make ad money, like Grammarly, Grammar Girl, dailywritingtips.com and the like.
Simply by virtue of mathematical probability, those questions were often addressed early in EL&U's history, and create many duplicates.
According to this SEDE query, the most frequently duplicated questions on EL&U are:
Is there a correct gender-neutral singular pronoun ("his" vs. "her" vs. "their")? - 17th question asked on EL&U
What's the rule for using "who" and "whom" correctly? - 19th question asked on EL&U
It shouldn't be too surprising that these highly duplicated questions are all very early questions and, in two cases, among the first 20 questions out of over 91,000. Their frequent duplication is not because "more time has passed" since they were written (logically speaking, that would ignore the fact that had the questions not been asked, their first duplicate would, theoretically, replace them in that rank). It's because they are questions that people wonder about a lot and as a result they got asked very early.
I know, none of this is surprising, but I just wanted to make that point before moving on to speculate about how this trend affects the experience of answering questions on EL&U over a wide span of time.
As the site progresses, the questions asked that are on-topic and not duplicates are increasingly likely to be obscure, to the point that we might imagine their obscurity being pinched up against some vague, blurry, unreal boundary where there are no more on-topic questions left to be asked. Of course, that scenario ("all on-topic questions have been asked--let's pack up and go home!") is never really going to happen to any subject, but the increasing obscurity of novel questions is certainly more likely to be a problem with a subject as relatively static as the English language (relative to, say, Stack Overflow or Computer Science).
So my question is, essentially, could this phenomenon be related to tchrist's observation that more questions are getting closed? Are there certain tags that are becoming more clunky than others over time? By my observation, it seems that many of the most upvoted questions today are etymology related or single-word-requests--both categories that, to some extent, are less burdened by the limits of obscurity. Is that noticeably different from what EL&U was like over different spans of time? Or am I extrapolating too much from the extreme examples of very early and very "frequently asked" questions?