For reading about this focus system you can read here https://phab.enlightenment.org/w/focus/
The current way of porting over was proposed by daveMDS:
Elm.win grabs for the keys for right left top down next prev, and just calls the move operation on the manager.
Each widget which currently handles focus needs to be ported to one of the focus types described on the wikipage.
If the currentl elm_focus.h stays as eo api after 1.18, we can migrate at any point later. The api can be adopted.