I remember a demo added to The ames Factory (the first one).
It showed various effects, up to fake 3D (based on sprites, similar e.g. to Mach Rider or F1 Race on the NES) and explained how to achieve such effect. It was quite like semi-interactive tutorial but in separate app. Of course sources were included. Those who have background in Clickteam’s products may know what I’m rambling about.
Maybe there should be something similar for GD?
Also with The Games Factory there was feature-complete game called Zeb (a platformer) with sources attached. I think we need some “open sourced” full games bundled with Game Develop and not only proofs of concept like current examples. Perhaps community collab (could make tileset)?