I know it's been discussed, but I think FabFilter could make a great metering plugin. The FF plugins that already exist have some of the best metering already, and I think the FabFilter plugins have the best overall look of all plugins.
I realized that I use a variety of meters for different tasks but I think FF could do it all in just one nice plugin. Here is what the meter needs in my opinion:
-Loudness Units (integrated short and long term that the user can define what is short and long term)
-RMS (like the Dorrough meters)
-realtime waveform scroll (like Pro-L)
-Intersample Peak/True Peak detection on/off
-Bit-Meter (See Wavelab 8.5 or Ozone 6)
-Frequency analyzer (like Pro-Q2) that can be hidden if needed
-Dynamic Range meter (see Brainworx BX Meter)
-Max Peak level needs to have an option to reset with the DAW transport, something overlooked in most meters besides TC LM2n. TC LM2n gets used a lot of me in audio post because it can reset when the transport stops and starts.
A safety net hard peak limiter ceiling like Waves WLM Plus. I usually set it to -3dBFS when I do post audio work. I don't rely on it for sound but it can catch a stray or random peak on long video pieces that are a rush job (no time to check every second o of the piece). It's a nice safety net and seems to be different than settings a normal limiter output ceiling all the way to -3.0dBFS.
Dither with auto blanking. I like the optimized and weighted dither options in Pro-L but I also like the auto-blanking you find in the Goodhertz and iZotope dither.
A way to display a log of overs on a given playback or render so you can go find the problem peaks quick and easy.
Finally, the ability to make the GUI big like iZotope Insight.
This would be my dream meter. I'm sure I'll think of a few other small things as well.