I was wondering just yesterday Bootstrap released the new official release of Bootstrap 4.0.0 (shortly after the pinegrow update)
When will you update bootstrap 4 files, and add the new examples as seen on https://getbootstrap.com/docs/4.0/examples/
Given that most of it is in place I am sure they will work to update to the latest. BootStrap was given priority over Foundation originally, now with the latest release bringing the Foundation update, I am sure they will get the current BootStrap addressed as well.