Generally Cook Builder is very close when these things happen normally there is a glitch or two but not many Admin works hard (Always) to stay ahead of depreciated functionality.
The current Cook on the edge build seems to work with very few problems on Joomla 3.4.8! and after popping over to PHP.net they seem to indicate that the transition aims at painless migration to the new major version and focuses mainly on removing depreciated functionality and improving language consistency
php.net/manual/en/migration70.php
So my guess is that the "on the edge build will most likely work on Joomla! 3.5 and PHP 7 out of the box right now but if all Cook functionality works with out a glitch i guess that will require some Cook community testing and reporting
Have you tried a cook Component on Joomla! 3.5 and PHP 7??