I agree with the idea of keeping it simple. We should have a 5 gallon system, since that is what most homebrewers would start out with. My personal feeling is that the mash tun should be based on a cooler, again since that is what most homebrewers start with. And the burners should be propane fired.
As far as whether it is gravity fed or uses a pump, it might be nice to have a system that could run either way. We may or may not always have electricity at the location we are brewing. So in those cases, we would want the system to work with gravity. But the pump option would be nice when electricity is available.
To go along with the brewing equipment, it would be nice to have a pictorial display of the brewing steps. These should be done professionally, on poster-sized board. We should also have available for display fresh grain, fresh hops, a grain mill, a chiller, the chemicals needed for sanitation, and other pieces of equipment needed.
I think the purpose of this system shouldn't be to show how good we are at homebrewing. It should be to show non-brewers how easy and fun it is to get into the hobby.
On Tap: Dusseldorf Alt, Kolsch, Hefe Weizen, Blonde, Chili Beer (Hot Blonde), Chocolate Hazelnut Porter