There is currently no public API alternative and no extension point for this functionality.
I would like to comment that this is somewhat invalid argument in this issue. Even if there are no ways to do something, it does not mean that our internal code may be used, especially if it was not designed to be API
Now for the root issue, what is the suggested way to handle this?
On the one hand, yes, it was Internal → Experimental by my request → and now Internal again
On the other hand, the functionality is there in my plugin, used by the users…
I am not sure how I should proceed with these cases, and what JetBrains expects me, as the plugin Author to do, remove the functionality from the plugin?