Child themes are not currently possible with the framework, but the framework is designed in a way where they shouldn't be necessary. All layout customization can be done by arranging widgets into whatever positions fit the layout you want, and using
Widget Context to show or hide widgets on different sections of the site if you want the layout to change.
If you're concerned about updates, all updates are done by patching the framework only, and should not have any impact on whatever customization you do to theme-specific CSS or code. Patch details can be found here:
Vertex Upgrade Patch