Is there BeOS somewhere?

QEMU in general translates so called "extended basic blocks", then later "chains" them by overwriting the jump instruction [simplification]. This doesn't work well with WebAssembly, because each EBB needs its own module and chaining would be hard to implement since we can't patch existing modules. This is why currently qemu-wasm is so slow.

v86 has a different model of "jitting" the code, but it only supports x86 and each new architecture would require significant rewrites.