It's great that we will (hopefully) soon be getting private channels but I hope that it will not stop with that. I would like to see them keep expanding the possibilities with channels.
Hidden private channel - Each member is invited and none else can see it.
Visible private channel - Everyone can see the channel but only invited members can see content. Good if you want people to be aware that it exists so they can request access if needed.
Channel with external members - Like above but users not member of the team can be invited e.g. guests or people helping the team out in a single project.
Open channel - Everyone can seen and join the channel but none is added automatically. Good if it is only relevant to some members of the team or if you only need it sometimes then everyone can manage their own access.
Published channel - Like "Private channel with external members" but anyone can join the channel without being part of the team. Good if you want to be able to talk to the team to ask them for help as a group.
Shared channel - A channel that is part of multiple teams so that you have a common area for two teams to work together without having to create a third team that has the members of both teams.
Anonymous channel - A channel that anyone can access and ask questions in without even needing an account. Good for support or interacting with parts of organization that do not have access to their own accounts. With a channel like this you would likely want the option to embed it in any webpage maybe even as a chat for talking with customers online.
Presumably the first one is what we will be getting around Oct/Nov but as you can see there are many more possibilities so I hope this long implementation period has helped them develop a good base they can keep building on.
Let's hope we at least get to hear something about this during ignite then. Would be nice if they regularly made some blog posts about what they are working on, then the community could help with some feedback as well.