I really hope that they do so. If I knew that I could get a 30kwh pack for about $6K, I would seriously consider keeping my 2015 Leaf for a long while.
You see the problem..by giving a roadmap now, they will hurt the sale of their 2016 30Kwh models. I had a 2013 model as well that I would have purchased with the $7500 discount they were offering on its residual, had a 30Kwh road map been announced for it, because I too believe in keeping my cars for a long time & to me a 100 mile range car is sufficient...I care less about a 200 mile range car.
I am pretty certain, no announcement of backward compatibility of the 30Kwh pack is more of a business decision rather than a technical one..and it will happen when the business environment is right for it.