This is definitely feasible in Bevy (either via Rust codegen, "interpreter-style" node execution, or scripting). And will be even more feasible once we have an official visual Bevy Editor. However I'm pretty skeptical of "visual / node based programming" and I wouldn't personally prioritize that work when we have so many other things to do. That being said, I'm guessing someone will eventually build a 3rd party plugin to do this.

Unreal's Niagara has a visual editor. While it is packaged as an VFX/particle editor, it is in many ways an ECS. Each particle can have custom data structure and modules/systems that drive them. Under the hood the graphs are translated to SIMD-optimized VM bytecode when run on CPU. It can even support translation to HLSL/GPU-acceleration if all modules support it. Not sure if Unity has something similar.