Ubuntu 16.04 is only about 6-8 weeks away from final release, and there’s still a debate raging about which version of PHP should ship with the distrubtion. At the moment, both PHP 5.6 and PHP 7.0 are present in the package archives for 16.04. However, the discussion on bug 1522422 suggests that only one will be supported in the final release, although there’s nothing official and conclusive to say which version will be chosen.
I don’t have any special insight into the Ubuntu development process, but personally I hope 16.04 will ship with either 5.6 or both. Shipping only with 7.0 will rule out a large number of sites still running on 5.x who can’t or won’t upgrade, and given that Long Term Support releases are aimed at people running servers I think that would be a mistake.