1.11rc1 is where PHP 7.0 support starts, its not finished. It is a release candidate.
Develop-next is going to be 1.11rc2 which ADDS more php7.0-7.1 compatibility.
Needless to say it hasn't been released yet.
My understanding is that the installer hasn't been updated for php compatibility yet, so you would want to install using php 5.6 and then you should be able to upgrade to php 7.0. I do not think that develop-next is ready for php 7.1 yet but I could be wrong. It is definitely not ready for php 7.2.