It's very refreshing and good to see WASM is embracing GC in addition to non-GC support. This approach is similar to D language where both non-GC and GC are supported with fast compilation and execution.

By the way now you can generate WASM via Dlang compiler LDC [1].

[1] Generating WebAssembly with LDC:

https://wiki.dlang.org/Generating_WebAssembly_with_LDC