Would be nice to see PHP 7 support with PHP7 released and Joomla 3.5 being released in the coming months.
The big item I know about is
must be replaced with name spaced
via
use Joomla\String\StringHelper;
Other items for good code clean up include things like
has been deprecated
use Joomla\Utilities\ArrayHelper;
Reference on this change requirement from the Joomla CMS
github.com/joomla/joomla-cms/pull/6600
There are also some specific PHP7 changes needed. most of which are BC compatible with php5
www.digitalocean.com/company/blog/getting-ready-for-php-7/