There’s not too much to the sdk. The idea may not even pan out since you can’t access other objects from the editor portion of a plug-in. Basically all the sdk allows is changing some properties of the current instance, drawing it, and running arbitrary js at some points.
So realistically you could make your own editor if you can pause the rest of the editor while a modal window was opened, since at that point you can do whatever you like, but there’s basically no interaction with the rest of construct.
Beyond the sdk everything is hidden with restricted access behind closures and such. And even if a back door could be found that is considered a hack, and it has a high chance or breaking between releases. Not to mention it bothers the devs since they go through great lengths to restrict access to avoid the possibility of rouge code crashing the editor.