We have recently moved house and DDs (6 and 3) were recently given the choice of having their own rooms or sharing. They chose to continue sharing.
In fact DD1 said to me that she felt sorry for only children, when asked why, she said, Daddys have mummies to go to sleep with, she had her sister to go to sleep with, and who did children with no siblings go to sleep with, and wouldn't they be lonely? She also pointed out that she wouldn't like to go to sleep on her own. I did point out to her that lots of boys and girls with siblings have their own rooms and go to sleep alone, and she thought that terribly sad and that they must be lonely. The mind of a 6 year old eh?
Honestly, mine love sharing, they never wake each other up at night when ill, the only bug bear for me is that one child will always wake at 6am, and then they'll want to wake up the other child so they can start playing. Quite often I have both children awake before 7am as a result.
When my children want their own rooms, we'll rearrange our house to make that work, but at the moment they're happy. I wouldn't worry about them being different genders either, obviously it will become an issue as they get older, but as you can easily give them their own room when they need it, I see no reason why not!