Hey, insane update! I briefly tested it and here are my observations:
When pressing 'add' in the plugin menu to add a person I am getting
in the console. But it adds correctly. EDIT: I think you need to press add twice. First time it does nothing, second time seems to work (tested with plugin in session plugins). Regarding bugs, I found one - when using copying left to right and using symmetry, looks like one side is always a bit higher in the Y axis (tested using default pose). So, by pressing copy left -> copy right, you'll gradually go into the sky with hands for example.
Now, regarding positioning.. world UI is definitely great idea, but we'll need something like rotation sensitivity like we had before (maybe in the plugin UI?). Also, when front facing your character it bothers me that going left with X axis moves your body part to the right (hopefully changeable with the code changes that's been mentioned, could also count as personal preference, but I strongly suggest making optional toggles for inverting as many axis as possible...). For quick posing, I think hotkeys + mouse will be the best, so space/ctrl/shift and mouse wherever in the world was much better for that. World UI for selecting body parts is awesome, but moving into the corner each time you want to position anything makes it more cumbersome. However, for fine tuning, separating each axis, as the new UI does, will be definitely very useful, so that's a great addition! I'd suggest remapping UI show key and add old controls on top of that.
Maybe try looking for Acidbubbles Keybindings integration in the future? I recall it's not that hard to achieve and it would be awesome. If you exposed your parameters to Keybindings, users could simply do their own key mappings for selecting body parts, changing modifiers, and maybe even swapping axis of mouse directions (I recall there are mouse mappings in keybindings). I believe all of that doesn't have to be keybinded at all for it to work, e. g. Timeline has lots of bindings that are unbound by default.