So there could be a separate option in the multiplayer, like a different tab, where you could see all of the people currently doing a replay in singleplayer.

With this function you could see if one of your favorite replay makers or buddies are making replays doing whatever, drop by, say something, chat with other people who are watching it, provide some tips and then leave and find another player doing replays or go on a multiplayer server.

Now the person making the replay would have op powers and be able to mute, kick or ban annoying people that could cause a disruption to other people watching.

This could help if someone was teaching a person on how to do replays by going in on their replay session and saying what they can do. It can also help if a famous replay maker wants to make an event where he is making a replay and people can watch it and talk to them and with others all in game.

Also, if someone didn't want people coming in he could go like /replay private and then the replay session wouldn't be able to be seen on the list. Someone could also set a pass so only people who know the pass word could get in, thus removing unwanted guests in their replay.

How about connection issues?
How much would internet lag if this would be implemented?
If it's minimal, i'm all for it. (even though i mostly fuck around in sp).

Well I guess it could all revolve around the connection of the host player i.e the one making the replay. Also if in peak times there are about 3-4 hundred people then I guess there would be around half that, probably less in sp.

Also it could be a check-able box whenever you go into sp and the default would be no.