Currently we have Teams defaulted to show you the first (up to five) channels ever created. If you want to add more channels to your left rail view, just click the ellipses next to the channel name and select “Favorite”. When you favorite the channel, it will then be “pinned” to your left rail under that team name.
Try that and let me know if that meets your needs!
The team has not made a decision on whether to move forward with this feature. We will update when we have new status to share.
We are working on a design with more density in mind. Until this design is solidified we are putting this item back to Under Review.