I remember I once saw someone say it would be nice to be able to paint the outside of a house. This is a similar idea. I was thinking it would be interesting if you could alter the style of house you live in. For example, if you live in the Shire you could opt for a Dwarven style house rather than a Hobbit style.
It would probably have certain limitations such as if you have a Standard house you can only choose from Standard house designs. It would also be nice if you could choose what layout you'd like for the inside of the house; an Elven appearance on the outside but a Bree layout on the inside.
I'm not sure if these kinds of changes are within the realm of possibility (and perhaps they've already been suggested?) but I think this could add a lot of diversity to the over all look of every neighborhood.