Well, just off the top of my head, it would be cool to allow users to select nips they want to support, but that would probably require the relay that's being used to have an easy "on/off" for those.
I think the lowest hanging fruit is really auto setting up ssl with domain.
Basically being able to simply put in your domain and have it do the Lets Encrypt setup or something similar.
I haven't put much thought into the details, just the overall "One click relay deploy" 😃