Never understood why these don’t exist for External-FX channels, would be really nice to monitor when doing real-time bounces.
edit
Another option would be to give the External-FX plugin Send and Return meters w/ clip.
Maybe because you can use an External FX as a plugin on any FX or Group channels. 
Right but sometimes those faders (post ext-fx return) aren’t at 0, and or the meter is post-fader. Would be nice if the plugin itself could have a send/return meter + clip level.