A few things to consider

-There are more than just those 3. But, even with just the 3. There is one site that will not do this. Maybe more. I'm not sure if all the mods here would be fine with it. Though I would generally be ok with it.

-One site has well over half the girl lovers I know that are active chatters banned. How would that work if the chat is held there?

-People use different sites for different vibes. We are not one collective hive mind. Working together is good. But, being different is also good. Some people like the vibes and people of different chats. There isn't a mono culture and merging them might actually get rid of people that liked the vibe of the one they go to.

-The one thing I could see is not having all the sites chatting at the same time. But, still you would have to overcome those rules. I suggest you post this at the other sites and see how this goes over.