I personally am curious. I am not sure how automated i would make it off the cuff. Unfortunately my ideas would have a sharp learning curve because i would make webmin an alternate "switchable" admin interface. moving to something like puppet or chef i think would be a better long run solution for administration (which is what i would really have to learn to make use of).
I also think that Debian might be a solid place to start. I think this is personally colored by my preference for Deb package management, and in this case I do not want to deal with any issues going back to Ubuntu changing something. Although if you wanted a supportable option they might be a good place to start.
Looking at JeOS might be a good place to go, OpenSUSE stripped down to bare needs and then you build up what you want. and you have their stability. but for ease of maintenance looking for a distro that has your preferred management interface might be the best option.