My girls have been sharing a room for a year now. They are 4 and 5 1/2. My older daughter has always been a great sleeper, while my younger daughter has not been. Honestly, I have mixed feelings about how it has gone. The pros (and largely the reason I opted to have them share a room) included my desire to promote closeness between them. In addition, I wanted to designate a play space for them to share some of the larger toys they had acquired - like play kitchen, doll houses, etc. I also wanted them to have to share space so that they would have more of an opportunity to work and play together. I didn't want them to always be able to retreat into their own space. Which leads me to some of the cons. It can be challenging when one or both needs some down/alone time (which we all do from time to time). Also, the sleep differences have not really gotten any better. My younger one does interrupt her sister's sleep quite a bit, waking her up earlier and keeping her up later than her past patterns were.
For a while we had our second room set up as the play room, which I really ended up not liking because they tended to just spread the toys further and further beyond that room. Also, it became harder to define personal property between them. Who's Polly Pocket was whose kind of thing. Now we are expecting our third child, and do not have any other options but to have a shared bedroom situation. While the toy room thing wasn't working for me in the form in which we had it set up, I do agree that having the bedroom be strictly for sleeping is a great idea!!! Now that I'm having another baby and our playroom will be a bedroom once again, I will have to reconfigure the playroom downstairs somehow. I am thinking I will get each girl her own toy chest to keep her "special" toys in to allow them a sense of ownership and individuality. But, as you have one of each, this issue probably won't be an issue at all. Also, we started the shared room at ages 3 and 4. Maybe if we had done it sooner, my girls would have acclimated their sleep requirements a little better. As far as when one is sick at night, oddly this doesn't seem to wake them. And often, we have the sick (flu sick)child sleep on the floor in our room anyway. If you have any other, more specific, questions about our experience, please feel free to message me. I wish you good luck.