1)Prefabs/Templates
It is convenient to build a GameObject in the scene by adding components and setting their properties to the appropriate values. This can create problems, however, when you have an object like an NPC, prop or piece of scenery that is reused in the scene several times. Simply copying the object will certainly produce duplicates but they will all be independently editable. Generally, you want all instances of a particular object to have the same properties, so when you edit one object in the scene, you would prefer not to have to make the same edit repeatedly to all the copies.
This Idea is given by Aekiro in the Idea Forum and it get 133 Votes
2)Scene Graph / Object Parenting
Implement a scene graph that allows building objects using a hierarchy of other objects.
"Rotation and scale of a group is applied to all child actors. Child actors always work in their own coordinate system, parent transformations are applied transparently." and ditch the clunky and unfriendly CONTAINERS + PIN.
This Idea is given by Salman_Shh in the Idea Forum and it get 78 Votes
3) Make Plugins inside Construct 3 using events
If i remember correctly when Ashley announced on scirra blog that C3 was coming he said something about users being able to create plugins using Construct's event sheet in the future.It would be pretty cool to have something like this so it would be more accessible to the community to contribute creating plugins.