I would also love to see Samba 4 in NethServer.
The NethServer team have done amazing work drawing attention to the project.
A strong feature like Samba 4 is headline grabbing and something most people looking for a Micro$oft drop in replacement or supplementary server are looking for.
Like it or not but we like in a world in which M$ own the vast majority of the desktop/server marketplace. Anything that can help bridge that gap is a massive win, and I believe in time will tip the scales away from M$.
On a feature by feature comparison against other distros trying to offer similar features to NethServer, they either have support, or are planning support for Samba 4.