You’ve raised a lot of concrete concerns.
Indeed the current AAX Wrapper JuceAAX_GUI makes it hard to implement something without a lot of refactor to JUCE.
So I’ve kept the less elegant ‘global flag’ patch. just because it’s a smaller patch and provides out-of-the-box support without special classes.
If you use your own parameter<>slider attachments you’ll need to add those nasty returns in your begin/end parameter changes.