I really like the idea of integrating gnome-boxes in Endless OS. In my case, I have been able to install Endless OS on several PC's with dual-boot with Windows in laboratories of rural schools in my country.
However, some school principals have asked me for this to be the main system considering a better implementation (eg buying private codecs) but it is not possible without allows support Windows (rebooting the computer doesn't work and is not nothing productive). Wine is an option, but it becomes complex in the short or long term, so virtual machines is the safe option.
Previously we had tried with fedora with equal results, but the vision of Endless OS together with its interface by far achieved better educational results.
At this point gnome-boxes would provide a simple interface only in use, since it is perfectly coupled with a gnome search provider and therefore a child could start a virtualized Windows instance as if it were an application.
Note: The use of Windows is due to specific applications granted by the government and that also work in outdated versions of Windows.