The idea is to group object by viewport and get that viewport in a map/proxy that will be the only things that get moved which would reduce the rendering cost of it. Of course this need to be done only when the speed of the scrolling allow for the additional redirection cost to an intermediate buffer. I would think that if the scroll speed is > 3 displays of an element on screen before it gets out, it makes sense to put it in a map/proxy.
If there is no scrolling involved anymore, but the item keep being redrawn, it should also be taken outside of the map/proxy. This is slightly more tricky as I have no idea how to detect that properly. We might need a new evas event to be notified when an object is being rendered. With the new event speedup infrastructure, it might not be to bad in term of performance. Will have to expirement.