It has dBFS on the main audio settings dialog, but I agree it would be nice if it had the readings on the main audio meters as well (although UI space is limited).

As for LUFS, I also would like something native to vMix. However, since that's something that's integrated over time, with different options available, I don't mind that they leave it to the user to install a loudness meter of their choice as a VST plugin. In my case, I use Youlean Loudness Meter (I am in no way affiliated with them), but I'm sure there are others available that work just as well or ever better.

One limitation of this approach is, the VST gets the audio pre-fader, so any loudness adjustments you make in the audio settings won't actually be reflected in the loudness meter VST. The way I work around this is, I just install a single VST on the Master audio channel, and just have a global combined LUFS meter. This does pick up any fader changes made on individual audio inputs. It works pretty well, especially since my main use case is balancing audio levels of multiple commentators, and having them show up in the same meter actually works for me. Of course YMMV.