As Freek Van der Herten mentions in this recent post to his site, it was announced by both Fabien Potencier (Symfony) and Taylor Otwell (Laravel) that the upcoming versions of the frameworks - Symfony 4 and Laravel 5.5 - will require PHP 7 by default.
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. 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.
Freek talks some about the improvements that come with PHP 7 and which he thinks will show up in the different frameworks' codebase. He sees this as "a message" to the PHP community as a whole that the migration to PHP 7 should happen sooner rather than later (and some of his own work to help reinforce this).