According to Fabien Potencier, lead of the Symfony project, the next major version of Symfony, to be released at then end of 2017, will require PHP 7.

#Symfony 4 (to released in November 2017) will drop #PHP 5 support... So, #Twig 2 stable should probably supports PHP 7 only, right? — Fabien Potencier (@fabpot) December 16, 2016

But Laravel will drop PHP 5 support even sooner. Taylor Otwell, the creator of Laravel, announced that Laravel 5.5, to be released in June 2017, will leave PHP 5 behind.

Laravel 5.5 in July 2017 will require PHP 7+ ? — Taylor Otwell (@taylorotwell) December 16, 2016

On multiple occasions Taylor et co. have stated that they don't like the strictness that things like scalar and return type hints bring to the table. So I don't expect to see them appear much in Laravel codebase. Smaller syntax improvements like for example the null coalescing operator will almost certainly be used.

A few weeks ago Jordi Boggiano reported that only a miserable 3% of all packages present on Packagist require PHP 7. The best thing about Symfony and Laravel dropping PHP 5 support is that it will send a strong message throughout the entire PHP ecosystem that you shouldn't bother with PHP 5 code anymore. When creating new projects and packages more developers will target PHP 7 as a minimum version as well.

For our PHP and Laravel packages we left PHP 5 behind as soon as PHP 7 was available. Our packages already make extensive use of return type hints, anonymous classes and the null coalescing operator to create more readable (and thus more maintainable) code.