I know this is a big one and perhaps impossible, but if it can be done it would be a killer app :-)
I have a harmony ultimate remote which also comes with a iOS app where I can select activities (watching TV, listen to.music, watch a movie etc).
Wouldn't it be great if this app could be merged with the official XBMC remote? The categories on the left panel should be your custom activities so when you select one the appropriate devices would be turned on and just like today the right part of the screen would show the available media for that activity.
Eg Music would turn on the receiver/amp and select the right input for that. The volume one the remote would control the volume on the receiver and all the music is shown on the right panel.
Likewise selecting Movies would also turn on your TV (which isn't needed for music) and show your movies...
And so on.
Activities/media categories should be customizable.