It is possible. In the Twitter Andrew Stanton canceled his words about the fact that the sequel to WALL•E will not be:
“@pixarishA113: @andrewstanton Will there ever be a sequel to Finding Nemo or WALL-E?” / Maybe...maybe not. (10th of February 2012).
He said there is a possibility of a sequel to Finding Nemo and WALL•E. After that, in the summer of 2012, he confirmed his intention to make Finding Nemo 2, which will be released in 2016. It is possible that his next film will be a sequel to WALL•E. If he wants to of course :)
John Lasseter said in spring 2012 that Pixar wants to create a sequel to WALL•E, but not it in the near future, because there's no decent plot for a movie. Pixar is likely to make a sequel to WALL•E in the future. At now company is busy producing other films. I hope that Pixar will find a good idea for a sequel to WALL•E and then will create it.