Earlier quoted context omitted.
None of these require a domain to work. There’s plenty precedent of things taking off without having a domain, eg Wordle, all Neal.fun sites, Hacker News, and I’m probably forgetting a few obvious ones. I know that “mystupidvibecodedidea.com” is all the rage but nobody cares if that’s instead on yourname.com/mystupidvibecoded idea except you.
Back in the day (~2003) it was popular to get a domain name for every project. Loads of people I knew where holding a domain name for every idea they had. I even had a few (~40). But in like 2008 I think I switched over to using just sub-domains of my primary. If anything took off I could then find and buy the cool name. And if it dies (likely outcome) I've saved $30.
My impression is that one of the social effects of domain names being cheap and easy to get (at least among many vaguely technologist-adjacent cohorts) is that failing to invest in a 2LD for a new thing winds up seen as tacky, sort of an “if you weren't willing to invest enough to put a cover on it then what does that mean for whether it's any good” thing (you could see it as a counterparty good-faith deposit versus attentional costs if you like). In some cases this goes down to the level of individual publications. Additionally the way social technology has wound up around URLs seems to mean that both longer URLs and artificially shortened ones wind up losing secondary reach in unpredictable ways. I'm not that fond of this trend but I can see ways it winds up making sense in context. I don't know how widespread it is.