Many GUI IRC clients do image / video embedding, even 10 years ago. Voice chat / video / screenshare is probably not a good fit unless you run some kind of secondary infrastructure like Jitsi and make it look like it's part of the client. Doesn't seem like a great fit though.

I know it is a different protocol, but doesn't Mumble provide this to some degree?

I feel like this is completely missing the point of what IRC is.

I appreciate its text-only nature and would never want to see image/video embeds and/or voice chat in my client.

Give Matrix a try.