Future of native-client after WebAssembly Post-MVP

Answering the side-questions only, because I no longer work on Native Client. Google's plans are its own to speak for, so I'll make this a wiki.

Update as of 2017/05/20 NaCl isn't in glibc. This was the original libc which was supported, and took quite a while to clean up and upstream. It was only ever supported by NaCl's GCC toolchain. There's still support for musl libc, which works with the more up-to-date LLVM-based NaCl and PNaCl toolchain.

Update as of 2017/05/30 the Chromium team announced the fate of PNaCl and tentative roadmap of WebAssembly features.

Here are some Native Client features which you haven't mentioned:

• Out-of-process, which many consider a bug because it forces asynchronous communication. It allows guaranteed address space, which with 64-bit isn't much of an upside, and was critical to Native Client's double-sandbox design. WebAssembly doesn't have processes yet.
• Has blocking to and from the JavaScript event loop, through postMessageAndAwaitResponse. Also seen as a bug by many.
• Has many APIs through Pepper. Many mirror the web platform's APIs.
• Can do memory protection through mprotect (though execute pages are limited).
• POSIX signals can be handled.
• Supports computed goto and other irreducible control flow.
• Has some Just-in-Time code patching support.
• Supports weaker than seq_cst atomics.
• Has support for inline assembly, as long as it follows the NaCl validation rules.

Not all of these are in Portable Native Client, though. There's official documentation of differences.

There's no timeline for any of the post-MVP WebAssembly features. We don't want to rush anything, but we want to deliver one the most useful things first. It's a community group, so priorities are really driven by whoever gets involved. Implementations won't be able to tackle features all at once, but exploration parallelizes well.