What is the feature you would like requested?

The ability to have ThreatClassic2 to be a tabbed entry on your Chat window that snaps in and can be clicked into focus depending on which tab is active in your chat window at any given point in time

Do you know of any other addon that has this functionality?

The chat windows are for chat messages, but tc2 displays bars in a frame. I don't think your request is possible, but maybe you can show me an addon that can already do this?

Yes- it's currently possible with Skada, even in BC Classic

https://www.curseforge.com/wow/addons/rakas-skada-chat-frame-integrator
https://www.wowinterface.com/downloads/info25146-SkadaClassic.html#info