Drysc also reminds us that the LFG channel isn't returning worldwide-- it'll only be available for those using the LFG tool. So while we haven't actually used it yet, that means you'll have to flag yourself as LFG, and then you'll get access to the channel.
But what hasn't been answered yet is whether you'll get access to a worldwide channel, or just the channel for your instance. It seems like just talking to people LFG for, say, Hellfire Ramparts is pretty pointless-- we can see their names up there on the screen and we can tell them anything we want. So that points to a worldwide LFG channel. But that then lends itself to the kind of stuff that made Blizzard ditch the channel in the first place, not to mention that it seems likely that tons of people who aren't actually LFG will sit flagged for LFG, just to listen in on the channel.
The problem here is that the best thing the LFG channel had going for it was the fact that it was an open area for players to listen in on LFG requests-- I could sit on my alt and listen for groups for my main, or on my main I could hear about a group, and then head to a dungeon that I had never planned to go to. I fail to see, however, how implementing the channel in the LFG tool, either local or worldwide, opens itself back up to that kind of ad hoc group forming. I guess we won't know until we get a chance to use it.