By my count there are two slots for a competition, and while I am not trying to chivvy anyone along, as I think that the effort of devising successful criteria is as important as the work entering the comp. I would like to see one, or more subjects that can be used “on table” as Wargame or Railway modelling terrain, rather than solely as a base for a diorama.
Thus, a building for wargames should allow the entry of “troops”, a house should allow figures to be placed inside, a drawbridge should open, or a defensive structure, should allow figures or vehicles to be placed on or within the feature, without tumbling over or balancing on the head of a pin. The feature should therefore be robust enough to withstand handling.
I would also like to see a competition showcasing a particular style of architecture, stone or half timbered walls, thatch or tiled roofs, a subterranean room, perhaps as part of a dungeon complex. There is also the possibility, though this may be limited in scope of restricting the model to a genre. Fantasy, Medieval, Roman or Contemporary. In this way people could showcase techniques for a particular type of structure.