This is already possible, albeit less convenient to do.
Here’s how to go about it;
- Toggle on the sidebar, if it is not already visible.
- Tap on the
icon in the ‘Channels’ header.
- Hover-over the header to force the icon to appear if you don’t see it.
- Tap on the
icon in the card of the channel you want to mute.
- Switch to the Settings tab if it doesn’t default to that (I would expect it to).
- There will be an option to mute the channel.
edit: Here’s some direct links for convenience;
edit 2: I do like the suggestion in the OP, FWIW.