Not sure if this is possible, but I would see this as a “nice to have” feature.
The idea here would be that, when you add a certain element (and the first element of that kind) to a page, Blocs auto-creates the necessary CSS class in the class manager.
Example:
You add a button to your page => Blocs add a separate “btn” css class to the class manager.
This makes it easier to create the necessary default classes to globally design all instances of that element, but can also provide a starting point to create variants.
You could also integrate this in Blocs Plus and based on the chosen cms, prepopulate WordPress-specific css classes. Or do the same for Volt CMS.
Hope my explination makes sense.