1) It's nonexistent so far, as far as I can tell, after years of research+work (unlike asm.js, which took one engineer a few months to implement a compiler for in Mozilla). Or can you actually use PNaCl in Chrome now? Or is there a concrete timeframe for when it'll be ready?

2) PNaCl involves pulling in all of Pepper, which is undocumented and very much tied to Chrome's architecture last I checked. Other browsers don't want to get on the "chase Chrome's Pepper implementation" treadmill. asm.js is just running in the JS VM, so talks to the DOM (and GL and networking, etc) in the normal way, which browsers already implement.