More than it not being possible, it's not regarded as desirable - IntelliJ users greatly value consistency. The fact that the experience is consistent across different languages is one of the things I like best about IntelliJ. Can you give me an idea of the sort of thing that you'd like to see that you haven't seen?
Here's an example of something I recently added (an inline inspector), that my main competitor (VS Code) said wasn't possible with the VS Code APIs: https://cursive-ide.com/blog/cursive-1.14.0-eap1.html. I have another major feature that I don't have good online doc for, which is also not possible with the VS Code API (parinfer, a Clojure editing mode). This gives you an idea of what it looks like, but this is old and my implementation doesn't work much like this any more: https://shaunlebron.github.io/parinfer.
Here's an example of something I recently added (an inline inspector), that my main competitor (VS Code) said wasn't possible with the VS Code APIs: https://cursive-ide.com/blog/cursive-1.14.0-eap1.html. I have another major feature that I don't have good online doc for, which is also not possible with the VS Code API (parinfer, a Clojure editing mode). This gives you an idea of what it looks like, but this is old and my implementation doesn't work much like this any more: https://shaunlebron.github.io/parinfer.