Linked text channels

I've used Teamspeak before Discord came out and during my transition over to Discord there was one feature I truly missed; text channels which are only viewable to those in a voice channel. 

Why is this good for Discord? 

- Sometimes, you only want to type to people you are talking to in a channel, with things that are somewhat private. For example, Phasmophobia codes. 

- If you're in a channel but don't want to use your microphone, you have no real way of communicating to the rest of them without flooding a public text channel.

Of course, if this was added it would be abled to be turned on and off.