It happened!
PHP 7.0.0 was released. That means that we finally can use all the new shiny features such as return and scalar typing, ?? operator, anonymous classes, safe random generation and many more. As a huge bonus, thanks to great job of the PHP team, we've got significant performance boost for free.
There's an official migration guide available in PHP manual.
Yii 2.0 is compatible with PHP 7 and should run on it without any issues. Yii 1.1 has some issues which will be fixed in 1.1.17.
Congrats everyone and big thanks to PHP team for pushing it further!