we kinda need some more keeps/buildings with interiors dont we?
You can actually very easily add castle interiors (the ones you see when you enter a castle in SP) as scene props. There's already one of the khergit castle interiors avaiable, I don't know why taleworlds didn't add the rest though (There are also prison interiors and some "tutorial scene" interiors that don't seem to be used in-game).
For example, if you want to add the interior of castle_keep_b (the big rhodok keep, seen in greipenfurt castle for example), just paste this at the end of your scene_props.txt :
spr_castle_h_keep_b_interior 0 0 castle_h_interior_a bo_castle_h_interior_a 0
and don't forget to increase the number of props by 1, at the beggining of scene_props.txt
Of course teleporting doors would have to be added in order to use these interiors, but they're worth it and there are like 100 of them in common res that could be used.