I completely get the value of designing in a live environment. That’s why I created PluginGuiMagic (dual license) in the meantime. It is a 3rd party module that adds the missing features:
- more signal visualisations (level meter, analyser, frequency response plot for IIR, can be extended)
- more LookAndFeels (to be continued)
- FlexBox layout
- CSS-like property inheritance
- editable without coding while the GUI is running
- extendable with your own components
- usable in JUCE plugins as well as applications
- for fast prototyping as well as GUI in production
The module you need to add to your project is here:
If you need help there is also a dedicated forum since I didn’t want to spam here too often 
https://forum.foleysfinest.com/
Hope that makes your life easier