First suggestion I have is to add all decoration tags(house floor, yard, etc) to all existing and upcoming decorations. This would not only allow more freedom in decorating, but also inspire new interior and exterior designs. As of right now, we can only place decorations outside or on farms if they have the "yard" attribute. However, what if we want to put wooden benches outside? Perhaps a bench sitting in a garden that we decide to maintain. By adding all the tags to every piece of decor, you ultimately add a large amount of variation to entries for decorating events in the forums as well. This seems like a minor change, but perhaps we can show off some awesome homes and properties that you can't quite achieve on Live. Let our imagination loose.
However, a distinction between wall and ground/floor decoration would be alright to keep.
Nutshell: Allow us to place any piece of furniture and/or decor anywhere we want on our property by adding all possible decoration placement tags to all existing and upcoming decor. Logical limitations can be kept such as the distinction between ground and wall decor.
Second suggestion:
Not quite sure how much freedom your team actually has for editing and creating items/effects, but imagine a new type of decoration where it is based around auras or enlarged visual effects that already exist in game. These effects would be like weather over an area for maybe an hour or two after activation.
For example, perhaps you can take the Stormcaller Staff(item id 21232) and use its model for a piece of decoration. Upon offering (enter item), it summons a storm cloud(area effect of...maybe 24x24 or just smaller than that) which stays for one hour or two. The functionality for this piece of decor could be reducing crop growth times by -10% or something, nothing too major.
This idea can be extended beyond weather effects as well. The models already exist for various trees and plants so to further add onto the variation of home/garden decoration, we can recycle those very same models into permanent features that only act as decoration; they should not yield any produce/items. Permanent greenhouses, cherry trees, and any other plants that look nice as decor would be a nice touch. Make the neighborhoods look nice!