Here's something I'd love for my house:
A shower that is big enough to bring my baby in with me - without her getting wet. Picture this: a little corner with a comfortable, rubbery seat and some appropriate playthings. That's for the times when I need to take a quick shower, but I don't have time to give the baby a bath too.
There would also be in option to convert that little seat into a baby tub and - you guessed it - there would be a little shower head that you could use to control the water flow. This would be for the times when I want both me and baby to freshen up.
Somebody, go invent this. Oh, and don't forget to give me the credit and a percentage of the profits if you make millions...
(Photo by: slight clutter)