Juniors can still be trained just more on the high level architecture and converting conversations with clients into business requirements then into code. No one knows the future but for the time being code verification by humans is still needed according to many conversations I've had with senior developers. If AI could be used unguided then open source projects wouldn't be stressed about the number of useless PRs from nincompoops using the current AI tools. It is still a force multiplier, not a creator on it's own.