WebAssembly is unrelated to PNaCl and has no limitations on the bit width of the host OS or the running program. PNaCl has those limitations because of how its

WebAssembly is unrelated to PNaCl and has no limitations on the bit width of the host OS or the running program. PNaCl has those limitations because of how its sandbox works, but WebAssembly does not use a sandbox at all- it uses Javascript's security model instead. (The WebAssembly MVP only supports the wasm32 target, but wasm64 is also planned.)