They're letting you know that your app is too good to be thrown away permanently (aka rejected) but that they already have their designated 'bucket' full of applicants full and will probably may not get to you.
Depending on where this school is on your wish list and what your status is, now might be a good time to ramp up a serious LOI campaign, just so they know that if they do look for more students to interview, you would be delighted to have the opportunity.