Yes, and there’s still support for theming IntelliJ - within the very particular confines on what constitutes a theme. And you can’t apply an IntelliJ theme on a random Swing app with its own custom components.
And what you are referring to is already supported by Material module and its components - using different colors, different typography, different shapes - and have it apply on the entirety of the app, as long as it’s using the Material components.