NaCl was CPU specific, and the way they solved this problem with PNaCl (by using a subset of the LLVM IR) was more or less a hack which most likely involved at

NaCl was CPU specific, and the way they solved this problem with PNaCl (by using a subset of the LLVM IR) was more or less a hack which most likely involved at least as much machinery in the browser as a WASM runtime (and it compiled slower and also performance wasn't any better than even the first WASM runtimes, the only thing that PNaCl had going for it was straightforward multithreading support, which took far too long to materialize in WASM - on the other hand, Spectre/Meltdown would also have affected PNaCl hard). Having worked with asm.js, NaCl, PNaCl (plus a couple other long forgotten competitors like Adobe's Alchemy/Flascc) and finally WASM: WASM is the natural result of an evolutionary process, and considering what all could have gone wrong if business decisions would have overruled technology decisions, what we got out of the whole endeavour is really pretty damn good. It's really not surprising that Google abandondend PNaCl and went full in on WASM.