It would be great to implement client side. I just don't know how the comment system would work. Do you post to 4 communities all at once? Obviously moderation issues if it's a single comment linked to 4 servers, but if it's not then people who don't have a client that combines duplicate comments on duplicate communities would see a bunch of garbage spam.
I guess I'm not saying it's inconceivable that this feature could be done well, but the obstacles seem really tall. I can't even imagine how I would implement this.
Sure, li'l buddy! He's coming quick, so I'm just going to run over there to take a picture.