Given how hard we thought programming was a year or two ago, I wouldn't bank my future on design being too hard for an LLM. They're already quite good at helping writing design docs.

Lol nope. When I'm trying to get it do make something big/complicated I start by telling it it's a software project manager and have me build a spec sheet on the design. Then I hand that off to an architect to flesh out the languages, libraries, files needed etc. Then from that list you can have it work on individual files and functions.