I see nothing inherently more efficient about PNaCl. Both it and WASM expose an architecture-agnostic 32-bit virtual instruction set, then rely on the user agen

I see nothing inherently more efficient about PNaCl. Both it and WASM expose an architecture-agnostic 32-bit virtual instruction set, then rely on the user agent to apply good optimization. WASM’s performance will improve. Non-portable NaCl did have the advantage that it could specifically target and optimize for one CPU architecture, and it had the beginnings of 64-bit address space support. These were nice, but not widely used. And we both could conceivably make it into WASM in the future.