Been working on a project that fits this description for the last couple months. Don't expect any of this in C2 at this point, but...
1. Translucent Inactive Layers is a godsend for working on a game with complex scenery, and also enables selective filtering when selecting objects/select all. However, there is no way I know of to select all of X type of objects on X layer. Selecting an object selects all of those objects in the layout, even when in TIL mode, instead of just those on the selected layer.
2. Wrapping objects (grouping an arbitrary selection to transform as a unit) is super useful. But...sometimes the rotation handle gets very wonky, ending up far away from the wrapped object, or even so far off the screen as to be unreachable.
3. In events, we can replace X object with Y object as long as both objects are the same object type, and share all the relevant vars/behaviors/effects for said events. There should be a similar option in the layout editor to replace objects with other objects, preserving size/position/frame/etc.