My wife and I have two daughters, age 4 and 6, and the 4BR, middle class house you would probably expect.
The girls have each been in their own bedroom for virtually all of their life. I definitely see the appeal of (perhaps forced) sharing and communication... but in practice, for most of their lives, one of them has been sleeping far better than the other. For example, the 4yo's current trick is to stay awake in her bed reading and playing for hours, with the light on, no matter how many times we come back in to tell her to turn it off. So we've really just kept them separate for their own - let alone our - sake, so that at least one of them can get to sleep at a sensible hour, without being dragged down by the other. ymmv though.