I just did it. Put my 13 month old into 3 year olds room. I lasted two nights before I swapped back. My stress levels went through the roof freaking out about one waking the other up.
It seemed like such a good idea in my head. But the 3yo likes to play bed iPad for half an hour before lights out and she couldn't do that anymore, and that was my 1 chance to eat dinner and shower.