Binaryen has a lot of baggage from Wasm early days, when it was still a strict AST. Many newer features are difficult to manipulate in its model.

In our compiler (featured in TFA), we chose to define our own data structure for an abstract representation of Wasm. We then wrote two emitters: one to .wasm (the default, for speed), and one to .wat (to debug our compiler when we get it wrong). It was pretty straightforward, so I think the instruction set is quite nice. [1]

[1] https://github.com/scala-js/scala-js/tree/main/linker/shared...