The Bash compatible syntax is just one representation of an underlying cross-language API. You can also write code in your preferred language, provided there's an SDK for it. (Currently: Python, TypeScript, Go, PHP, Java, Elixir, Rust, .NET)
But if you're talking specifically about shell or a "native" REPL in a safer language - I also want to scratch that itch. Some day I'll dust off https://github.com/vito/dash :)
What you aren't including is the chronic cost of maintaining the status quo, which is the entire reason for making the change. Sometimes making no decision costs you more than making a risky one - and if the decision is risky, you'll want to investigate it first.
During that investigation you discover things (like having to implement your own components) and try to account for how much they'll subtract from the time and energy you save. If the calculus works out, you keep going. If it doesn't, you stop. We kept going, and now we can ship complex features and optimizations to both UIs within a day or two.
The compiler will tell you if the types aren't compatible, and this is only for primitive comparable types. What `min()` implementation could you have that even does something different?
But if you're talking specifically about shell or a "native" REPL in a safer language - I also want to scratch that itch. Some day I'll dust off https://github.com/vito/dash :)