First of all, let me say thank you for your amazing software!
Let me just share some thoughts, that can improve it even more.
I have a huge experience in 3D rig and animation, mostly in Maya. There is one simple but really efficient thing you can do any type of the rig with.
It is Driven Key. The principal is making dependence between different attributes. For instance, Y-Translation of the object N1 can affect XYZ Rotation, or any attribute/attributes, of object N2 or bunch of objects.
In case of the Spine, it will make the ability to do a complicated animation of points, joints driven by a single controller(another joint or slider). You can mix a couple of drivers. So you can, for example, make not 2.5D animation but full 180 or even 360 degrees 3D animation of the head. You can make 2 drivers, first one- is changing the head shape side-front-side, second - top-front-down. It is driven by 1 controller in the viewport(by the translation attributes) or what easy is sliders in the UI.
And it is just one simple example of the usage of the Driven Keys.
Thanks!