Sorry, yes, I meant PNaCl.

> I don't see an issue with shipping uArch specific assembly, nowadays you only have 2 really in heavy use today,

That is true today, but it would prevent other architectures from getting a fair shot. Or, if another architecture exploded in popularity despite this, it would mean fragmentation.

This is why the Portable version of NaCl was the final iteration, and the only one even Google considered shippable, back then.

I agree the other stuff is fixable - APIs etc. It's really portability that was the sticking point. No browser vendor was willing to give that up.