Just to be pedantic, it's "illegal" to hoard IPv4 or to buy it for any purpose other than using it directly. But yeah, in the real world it may become more financialized than it already is. OTOH if prices keep dropping maybe they won't bother.

Ford Motor Company has both a /8 and a /9. They own over 16 million ip addresses.

Relatedly, I've been seeing some people buying up old domains and squatting on them with AI generated content. Not even ads, but content that seems like something that might actually show up in a rare Google search query. Not really sure what the play is or why this is better than advertising the domain for sale (do registrars punish overt squatting these days?).