I don't know about the millennial angle, but minimalism does seem to be on the way out. As a university teacher, I spend a lot of time staring at the lids of laptops (as much as I'd like to ban them).

Back in the late 2000s, those laptops would be covered with various stickers -- Obama, sports, home star runner, etc. The last decade or so they have just been shiny unadorned metal or plastic.

This year amongst my 18 year-old students, the stickers have started coming back.