Listed in no particular order are things that need improvement upon...mostly while trying to replicate my house.
Dressers - There isn't any. Where am I to store a change of clothing?
Hung Clothes - Speaking of clothes maybe there could be some to hang up in a closet?
TVs - Turned off or maybe flickering some static images. A few different sizes of TVs would be nice for those of us who want to give it that modern life feel.
Carpets - Like the dressers there aren't any. Mine is an indoor/outdoor carpet that's dark pink/purple. Something worth keeping in mind so that all carpet doesn't end up as "fluffy."
Beds - The available beds look to utilitarian, or like something only a destitute person would sleep in. Can we have something more comfortable that would not give a restless night's sleep?
Mirrors: Good for bathrooms, and one's own personal fun house.
Grass seeds - Self explanatory. Grass doesn't grow back, and we need something to fix that.
Biomes - I have yet to see any. An island or two would be nice for those stand-alone projects.
Color - There is a limited amount of color combinations to choose from. Is there some way to incorporate a slider that will allow you to change the color of a block or object to something more fitting?
Arrow Keys - Would be useful to cycle through the menus. Up and down keys to change your main selection while left and right would be used to cycle through the various colors/shapes.
World Editor - Unlikely to happen, but still, nothing says frustrating like tearing down a wall just because you need to move it a dozen or so blocks to the right...also useful in flatting out the terrain, because let's face it, minecraft this isn't, so kiss getting a leveled area good-bye. Also, in terms of updates to the main program, this can be useful to save buildings that took hours to build. As you can imagine I do not want to rebuild my house a second time unless I absolutely have too, so yes, this will be useful in saving a number of user's sanity, and cut down on the cost of broken monitors, controllers, and visits to the ER.