Kept out of sight in this rogue essay is the classic question: Who's your audience?
If you're writing for yourself (and maybe a very small number of equally erudite readers) cut loose! Embrace "anfractuous density and heedless flamboyance." But if you're trying to change people's minds, or share knowledge widely, everything in this essay is defiantly at odds with what's necessary to get the rest of the world to pay attention.
does anyone need to get the 'rest of the world' to pay attention? That's already a crowded market of questionable characters.
There's something ironic and self-defeating in trying to write to the whole world while also having such a low opinion of the whole world that a writer thinks they can't express themselves the way they want to or lose their audience.
As DBH says at the end of the essay, don't write down to what you presume to be the level of your readers, that's insulting to both you and your readers.
Kept out of sight in this dismissive comment is the pressing question: What year is it?
Up until four years ago, your notion of "what's necessary" was the law of the land. Starting from sometime around Hemingway, we produced a century's worth of flattened, easy-reading slop, and much knowledge was shared very widely. There was a certain art to the blandness. (One notable master of that art is pg, the creator of this website.)
Then we fed that slop into a giant machine that makes it trivial for anyone and everyone to produce that sort of generic writing. If you want to change minds and differentiate yourself now, you can't just do the old flat style anymore. You have to set yourself apart somehow, and you can start by loving the craft of writing again.
The people who matter will read it and love it. Everybody else can take what you wrote, dump it into the slop machine, and rearrange it into something they find easier to read.
What's interesting to me is that the examples he gives are beautiful because of their sincerity. Even if there is artifice, or they're being formal or playful, their style reflects their reading, their shared culture and of course as you say their audience - which I think for them was a very small elite.
Anyone who writes in a flamboyant style now - as the essay's author does - necessarily comes across as a kind of pastiche. There is something camp or affected about it. Maybe that can change. Maybe a new flamboyance can develop. But I think his antiquated style of flamboyance is unlikely to come back to real life.