Add ability to tell which channels are "active" or "popular"

Maybe this is more of an issue request. We once had the site more "open" so that anyone could create a public channel. Quickly, the site was flooded with public channels. Most of them were quickly abandoned. It became impossible for a new user to look at the channels and figure out which ones were active. So now, we've got it so only a 'mod' can create a new public channel. This has led to not a lot of new channels being made. It's a little non-ideal.

Is there a way to let it be open so anyone can create a channel AND easily tell which channels are popular? Maybe by

1. displaying a number saying how many people have joined the channel and/or
2. having a a color indicator saying how many messages have been sent in the last week?

No files, tests, or entry points are named. Start by locating public-channel creation and channel-list presentation, then clarify which popularity signal and display behavior should be selected; done means the agreed signal is visible and the resulting behavior is covered by the relevant tests.