My plans for NGUI are simple: I'll keep using it, and as such I'll keep adding to it. I'm not saying the support will end at the end of the year, I'm merely saying that I will most certainly be using it until the end of the year, meaning there will be updates coming. After that, depends on what I'll be doing and on how uGUI is received.
I actually had a look at uGUI last week with the idea of making it possible for NGUI to use its functionality. Unfortunately with the amount of recent changes over the last year it wasn't a simple undertaking by any means. The way certain things were done makes meshing them together difficult. The way draw the order is handled being the main one. NGUI gives a lot more control here, and a child sprite can be drawn before its parent if so desired (think: shadow). This isn't possible in uGUI. If there was a way to specify depth on canvas renderers, then everything would merge over smoothly, but the way things are I can migrate a UI from uGUI to NGUI, but the other way around is not so simple.
I will likely add a new widget type soon that will be like an NGUI sprite in terms of its functionality, but will be drawn by a uGUI canvas and then see from there.