You can do this now via command maps. It's not pretty, but with backend programming, you can do just about anything.
If you don't want to create complicated maps, you could accomplish the same thing via a MLCycleStates button on the TVLobby screen. Have the button set a variable, and based on that variable, send the IR to whatever device you want.
I agree it would be a nice feature, but you can workaround it today if you need to.