Well, what is actually needed to make a game engine/editor? Be able to draw stuff, get mouse/keyboard input, a way to do the logic to put stuff together, and finally a way to read/write files. Not all vanilla construct features are well geared for much of that, but it would depend on what features you'd want your game engine/editor to have.
Say you wanted to make an engine much like construct. The layout editor and event editor would mostly be a lot of busywork. Same with the runtime. Drawing images or dynamically loading images are some drawing primitives that may need additional plugins. It could take some strategy to keep stuff organized so you wouldn't get bogged down with too may events to deal with.
In the end you may be fighting with constucts features to do what you want, so it may just be worth it to do the engine something lower level like js so there is more control and less friction.