I'd like to see stand alone castles. The new ones are difficult enough to do anything with as is, but when certain pieces don't even work without having to sit on a big rock, it really reduces what you can do with them.
It would also be nice to have to have a base plate for something like the chapel? in 6000 so it can be used as a stand alone building. Actually that's something that I'd like to see in playmobil, though it may be considered to macabre to be produced. A graveyard. Baseplate with cobble path and holes for inserting headstones, fences, trees etc. Make the baseplate modular or at least compatible with the baseplate I suggested for the chapel.
You could also have a modular baseplate system for doing something like an amusement park - mini-golf, garden etc. I think mini-golf would work well, each plate would have a different hazzard on it and an actual ball would be used to get through the different hazzards.
Anyway enough rambling, but I would like a graveyard...and an angry mob.