Yeah the biggest differences between our chat channels and guilds are that (a) there is no "invite" barrier to joining the channel, (b) channel bans have limited effectiveness, since they reset whenever the channel empties, and (c) we can't change servers without a complete reroll, which really discourages people from searching to find a "guild" they fit into well.
AP is crowded enough to support guild-like private channels on it, I doubt any of the other servers are. Joining an exclusive channel keeps you from seeing what's going on in the main channel though, and I doubt there's enough interest in private channels to make multiple channels a feature worth adding (imo).