I'm working on another castle/fantasy landscape display. It'll be big, bigger than last year's, but it's not going down to the floor this time. (Instead, it'll go UP!) It'll fit fine in a collaborative display, but if we have the same space as before, it'll likely span the whole depth of the tables, so any collaborative sets can connect on the sides.
I'm planning out how to do the build, but probably won't have details until I'm nearly done.
If we're doing a collaborative display, I'll build/bring parts for filler, and try to have roads, cliffs, rivers, etc. that can join up and hide borders.
Personally, I think a collaborative display would be more interesting if it has some kind of theme or story running through it, even if it's just a common element repeated in different areas. It doesn't have to dictate exactly what people build, but it can help define the display as a whole.
My thoughts on a theme is either some distinctive creature milling around each area causing trouble, or maybe a decorative building motif or image, zombie invasion, or some other thing that is simple enough for anyone to incorporate. I dunno, it's an idea.