This contains some gem ideas. My 3 cents:
Add a tween behaviour. I know there's a couple of 3rd party plugins, but I mean something a bit more substantial... One you could incorporate into a sprite/variable animator (like the one in Godot engine or a better version of the animator in Unity). Imagine an animation behaviour where you could easily animate anything, with tweening. Because that's what I want to use and have to create every time I want to do something in c2, even if it's just to animate a button effect or a layer opacity.
Oh, and give us access to full box2d because the demo physics plugin is OK for creating a quick game demo but, strewth, it's frustratingly limited.
And what newt just posted too. I would love to create my own plugins but if I'm going to bother to learn to write code then that defeats the point of using a no-code engine. Just imagine a Blueprints style of plugin creator... Mmmmm.