I found Pharo's (Smalltalk's) image based programming environment interesting when I played around with it, but I'm not sure how well it'd play with an agent-first workflow, or whether it'd bring any advantages.

One thing that AI programming has done is made me care more about how well the AI can handle a language than my own facility with it. I wouldn't be surprised if programming languages begin to tilt toward being easier for agents to work with, while still remaining readable to people -- whatever that ends up meaning.

I've found most agents can work effectively and quickly with Go code, I think mainly due to the strong focus on simplicity in the language and tooling. Something like Pharo is a bit like the opposite end of the spectrum.