During the 6th and 7th week of GSoC, i was working on adding the the ruler related callbacks in lokit, the progress has been slow but will try to cover up in the coming week.
For most part this involved a lot of code reading related to swruler, svxruler and ruler. As of now the callback that relays any ruler related change has been implemented and currently i am trying to implement the ruler in gtktiledviewer, specifically to fetch the current state. Once that is done, i will move towards implementing loleaflet support for ruler.
I don't think there should be much difficulty in working on this. With my current timeline, it would be difficult to do this during the gsoc period, but i could certainly work on this once i am done with the gsoc specific tasks.