As Aaron notes, PHP7 has significant speed improvements on past versions, and it will be great to be able to use it right away. WordPress unit tests have been running against PHP7 for months now, and all issues that came up have been settled. Some hosts are already testing (or even running some production sites) on PHP7, and I think it'll get quickly adopted by the leading managed hosts.
As Aaron closes the post, WordPress wants to support the latest technology, but not by forcing users to upgrade. They'd rather work with hosts and make upgrades safe and available.
Even as WordPress Core continues to expand its support for new versions of PHP, we have no intention of abandoning support for older versions until usage numbers show that the impact on users will be minimal. WordPress will continue to work with hosting providers to encourage them to upgrade their users to a current version of PHP and, when it’s reasonable, we will consider raising our minimum requirements. Regardless, WordPress continues to encourage all users to run the latest and greatest versions of PHP, including PHP7 upon its release.