Yep. Which is why targeting for any specific set of "values" or trying to capture the "latest trends" leads to problems. I mean, it is one thing to broaden the scope of what D&D is, quite another to say "D&D is now about Y and no longer about X."
I'm reminded of some advice a literary agent gave, which is not to worry about trends, whether your work fits in with it or not (or worse still, trying to adjust your work to a certain trend that you have little or no interest in). In fantasy literature, new trends generally don't mean a sea change as much as they are a broadening of what fantasy means. The old stuff doesn't go away. So for instance, when "grimdark" became the thing, it wasn't like all of a sudden all other tones of fantasy stopped being published. There might have been a few years where grimdark took up a larger percentage of market share--at least apparently so--but then the wider genre adjusted and integrated grimdark as another thematic sub-genre.
Furthermore, people change. A person's values and worldview at 30 or 40 is probably (hopefully!) not the same as it was when they were 16. This ties into another reason why going for the current trend is not recommended: by the time you get to publication, things might have moved on.
Or to put it another way, I think the best way forward is "both/and" not "either/or." Meaning, you can play traditional style D&D and kill things and take their stuff, or if you want to roleplay magic masquerade balls and academic politics, we'll provide that too. D&D is now big enough for a big umbrella approach.
But for that to be successful, two things have to happen:
1) WotC has to honor the big umbrella, and publish a range of thematic offerings.
2) The fan-base has to accept that not every product was written with them in mind.
I think the former is more likely than the latter.
Agreed with all of this--especially the point about how people's priorities change as they progress through life. Supposedly we all go through a new life stage every seven years, so what the core audience values now, will likely shift over time.
WOTC has produced tons of splatbooks expanding player options, but not a lot of expansion support for DMs. This is probably because everybody buys the player options books, but more DMs than players will buy DMs Guides, resulting in less sales.
5th Edition is a pretty flexible game system. I can't see why WOTC can just put out a book of "Game Modes" for D&D, with tutorials on multiple approaches to play. Then, write up a chapter teaching how novice DMs could DIY their own setting, put together using templates provided in the book.
You could have a chapter on each genre or play style. This could serve to include your entire player base, encourage them to try out different kinds of play styles under the "D&D Umbrella", and capture all of the customers. This would also increase interaction between groups of players, and introduce cross pollination of play styles and bring disparate players together as groups tried out each others' games.
There could be chapters on short term campaigns, and running very long campaigns. You could also have an introductory rules set, intermediate and hard mode. The hard mode could increase player mortality, and up the challenge in general, for players who are less casual and enjoy beating challenges as a team.
Genre chapters could include: Gritty Swords & Sorcery play, Planetary Romance/Science Fantasy play, CW-style fantasy teen relationship play (which I think is what Strixhaven is), Epic Heroic Fantasy, Classic Dungeon crawls, Crit Role style comedy romp/set piece action sequence games, Mysteries (like Candlekeep), Historical Realism or Arthurian Romance.