They're proposing essentially that: start at the 24th slide http://www.slideshare.net/zerutreck/taking-php-seriously-kei...

The smart part is that it's opt-in so you could gradually migrate a large project in-place. The only question would be whether they've broken compatibility with standard PHP or if it's simply stricter — it'd be really easy to get major projects to switch if it was like JavaScript's "use strict" where you can develop in strict mode but run on a legacy runtime.

I'll have to take a look at the Hack language. I've always wanted to try PHP, but I've always been deterred by the cruft (same reason I avoid Java).

That would probably result in the same situation as what we have with Python 2 and 3.