This is incredibly hard to do simply because apart from being able to interact with objects, picking up keys and having things play animations (which we already have in GG) these things are immensly complex.
The reason why most games in general rely on exploration and combat is because its simply easiest to do in an appealing way. Creating interesting puzzles or meaningful interactions with characters however is challenging to achieve and its very easy to either bore the player or make it awkward. It would be incredibly hard to create blank systems to build upon for that. (Unless you mean basic stuff like you see in the RPG Maker editor where dialogue is text based and the inventory also rather simplistic... I think we'll have that eventually built in)
Try the store. There are collections of scripts that should help you get started. I recommend the interactive environment pack by rolfy. I'll use it in my game as it too has a strong adventure game influence. I have seen several people code very compelling inventory systems as well.
The reason why GG has more developed FPS features than others is because it started as "First Person Shooter Creator Reloaded" 5 years ago and eventually opened up to other genres later down the road. However working in a genre akin to Myst will require LUA. GG has no templates like modern engines, you would just have to gather scripts that allow you to achieve what you can do. The people on here are very helpful when it comes to that.
A drag and drop type interface for an adventure game will likely not happen soon.