I hope I understand correctly but you need a desktop for a server environment? Even with Zentyal I never ever used the desktop environment and I was very pleased they finally came with an option to install without a desktop. Using the webinterface combined with SSH was more than enough to maintain any Zentyal server. I think the same counts for NethServer.
IMO a server should just serve. It should be almost invisible, transparent for end users. At the same time all services provided by the server must be stable, reliable and always available. In such a case, enduser don’t get to work on the server, only with the services provided by the server. And as a sysadmin, you don’t need a desktop environment on the server. So why bother having one?
The ONLY server that really needs a desktop is an LTSP server (for obvious reasons).
I mailed you privately about LinuxSchools project. I feel very reluctant to talk about another project with more or less the same goals and target audience in these forums since I don’t want to deliberately move members to another project. However, since LinuxSchools project is already 12+years old, very actively developed and especially aims at educational environments, it is a lot further when it comes to educational features. I am happy to tell more about this privately, but I am not going to advertise this over here.