I may have misunderstood slightly, but I think what you described is essentially the idea of Map From Base, just with a specific theme. I'm not sure either that or Map From Layout would work great with a theme requirement because you would end up with a lot of very similar maps.
For reference, I consider the types here to be:
- Map From Layout (but not necessarily with floor heights spelled out)
- Map From Base (I know there's been a better example in the past, but I don't think it was an official compo and thus I couldn't be assed searching for it. Basically that idea but with more freedom of structure/detail)
Restrictions are nice, but after a certain point I feel they hinder creativity more than promote it. It's just a matter of balance between freedom and direction. I like Map From Layout because it sets one up with a clear place to start, but leaves everything beyond that up to the mapper.
... Everything else aside, the community has been clamoring for a new official competition for 3 years now. If the power to create one has to be given to someone else (temporarily if need be) for it to happen, perhaps that is something to consider.