Rust isn't inherently slow to iterate, its just easy to write code that compiles slowly if you aren't careful. One of Bevy's primary focuses is to have fast iterative compile times. Changes to our examples can be recompiled in ~0.8-3 seconds (according to your hardware, os, and linker). We have a "fast compiles" configuration that works quite well.

First we do plan on exposing hooks to allow scripting languages to be plugged in to Bevy. We actually already have a pull request out for that.

However my default answer to the scripting question is that it is a non-goal for Bevy, and is in fact maybe even an anti-feature. I want Rust to be the "one language" people use to build Bevy games. I think a cohesive ecosystem is an incredibly important part of an engine's success. If half of Bevy devs use rust and the other half use C#, then compatibility and interop become a huge problem. The Rust language choice does set a high bar, but Bevy doesn't need to be all things to all people. Additionally, the Bevy API is a Rust API. Defining FFI on top means we need a second api surface that is the "lowest common denominator" (aka a C api). This both increases maintenance burden and creates the "rust experience" and the "everyone else" experience.

In the near future 3rd party Bevy scripting plugins will start popping up, but I doubt I will ever officially endorse them.

The developers of EVE Online had this same thought, about C++, so they used python as the gameplay scripting language. A few years later faced with unsolveable performance issues with large scale battles they had to resort to slowing down time by a factor of 4, during large scale battles.

Just a single anecdote but can be important to keep in mind. As well, some types of scripting languages can have their own productivity problems as projects get large. Lack of types making code hard to follow, bugs harder to track down, refactors riskier etc.