Why don't you go right to the source and ask the author herself? I've pasted in the Source section a link to her official web site, were you can find info about the series and about the author's plans for future books.
Meyer's draft of the "Midnight Sun" manuscript was posted on the Internet without her permission, so she has decided to put off finishing it. According to Meyer, she is "too sad about what has happened to continue working on Midnight Sun, and so it is on hold indefinitely." Apparently, she is taking a break from writing anything. She explains in the same note to her fans:
I only hope this note will stop all the confusion and online speculation so that the Twilight universe can once again become the happy escape it used to be. After this incredibly busy year, I am now focusing on spending more time with my family and working on some other writing projects.
Considering how quickly she wrote each of the four books, she probably needs a little break. Visit the sites below for more information. And do try to contact the author; she might just respond back to you! :)