In UI, I’m pretty sure that replacement is already here. We’ll be lucky if at least backend stays a place where people still care about the actual source.

I'd say the opposite, the frontend code is so complex these days that you can't escape the source code.

If you stick to tailwind + server side rendered pages you can probably go pretty far with just AI and no code knowledge but once you introduce modern TS tooling, I don't think it's enough anymore.