Yes, currently most of the developers are working on PHP5.5 environments but our QA happens in both PHP5.5 and PHP7.0 environments. We write forward compatible code which often requires not making use of some handy language features introduced in PHP7. We also deal with deprecations as they are announced. The framework is vendored and we make updates as needed - we also pull fixes from LExpress/symfony1, a community-driven sf1 fork that is still active. I'd like to add
github.com/wimg/PHPCompatibility to CI, that would be really useful in order to detect incompatibilities early.