I had queried Brad Wilber at the Chronicle of Higher Education with a list of made-up compounds in fantasy: UNOBTAINIUM, KRYPTONITE, DILITHIUM, ICE NINE, MITHRIL. He said it was too much of a list puzzle (imagine that!) for him, but UNOBTAINIUM would sure make a great themeless seed.
I don't make many themelesses these days since everybody and their brother submits a ton of them to Will. Plus, I think it's a much more interesting challenge to come up with a great theme. But when I heard NERD CULTURE in an audio book, I quickly counted it out (stupid compulsive constructor's brain, just let me listen to the book already!) — 11 letters, the same as UNOBTAINIUM! Felt like a mini-theme I could get behind.
Unfortunately, 11 letters is a terrible length to work with in a themeless. It's so stubborn, forcing placement of certain black squares right off the bat, draining flexibility. I tested dozens of possibilities, all of them leading to some dead-end or requiring 70+ words (that's not a very interesting construction challenge to me), before finally arriving at what you see.
I wasn't thrilled about three middle entries — PERSIANS, CADENCE, SANCTION, but each felt like there was possibility for good cluing. SANCTION, for example, is a word that can mean one thing … or its opposite. (I clued it as [Approve … or prohibit].)
The upper right took hundreds of tries before I finally felt that the result was sparkly and clean enough ... with one hesitation, anyway: I love ASCII ART, and it fits great with the NERD CULTURE mini-theme, but would solvers struggle with the SIRENIA (it's the order containing manatees) crossing? I love that SIRENIA term, derived from the Sirens of Greek myth. Hopefully, people who don't know ASCII can think about the term "Animalia" and get the -IA ending that way.
My original clue for ANACONDA was [Sir Mix-a-Lot's "don't want none / Unless you got buns, hon"]. I was pretty sure Will wouldn't be able to use it for the NYT audience. But I had to try.
Shout at to BRAD at 26-Across! Thanks so much for the idea.