I really like the idea of pi-hole but it take control of the whole server and this behavior doesn’t play well with NS, as @Jclendineng correctly pointed out.
I’d say quite big. I like the idea behind containers (Spethane and Davide are trying to integrate Docker). But when you have a container, it’s like a black box.
I’d rather work with pi-hole developers and try to integrate is inside NethServer (including the awesome web interface!).