As our recent blog post indicates, the Demonstration site is alive and well. I can't speak to the particulars of the demonstration you submitted, but have asked our team to investigate and comment. And yes, we had some behind-the-scenes infrastructure updates to handle for the V10 transition which did slow down our processing of submissions for a while. The blog post does also allude to our goal of making demonstrations function in the Wolfram Cloud. More details on this will be coming later.